I see that the mod deleted a lot of comments here. I'll try to be as objective as possible, and to not refer to anything after 1999.

"Why did the NATO countries care about Yugoslavia?"

-- Largely because of the Bosnian conflict, which had shocked the conscience of Europe. To understand Kosovo, you need to start with Bosnia.

At the time, it was believed that over 100,000 people had been killed there over a three-year period (current estimates are a bit lower, closer to 90,000). The Bosnian war had also seen the protracted siege of Sarajevo, a peaceful small European city that had hosted the Winter Olympics just a few years earlier, with gruesome scenes of destruction and suffering beamed directly into European media. And then of course the conflict had also included mass ethnic cleansing by all sides; the institution of "detainment" camps that were unpleasantly reminiscent of the concentration camps of WWII; and several horrific massacres, most notably at Srebrenica. About 600,000 Bosnians were refugees (out of a population of just 4.2 million or so); of these, about half were spread across Europe, with another 10% or so going to the United States and Canada. At the time, these were the largest refugee flows Europe had seen since the 1940s.

Of course Bosnia was not the only conflict in the former Yugoslavia. The early 1990s had a brief shooting war as Slovenia seceded from Yugoslavia; the creation of two breakaway Serb "republics" on the territory of Croatia; the near complete destruction of the city of Vukovar; and massive damage to the coastal town of Dubrovnik, a cultural landmark that had also been a popular vacation destination for many Europeans. However, by early 1995 Bosnia had been the main center of violence in the former Yugoslavia for some time, and it was Bosnia that focused Europe's attention, with non-stop coverage by European print and broadcast media, and a great deal of public attention and indignation.

Rightly or wrongly, the Milosevic government in Belgrade was widely perceived as the main driver of the conflict. Certainly Milosevic's government was supporting the breakaway Serb regions in Croatia, and also supporting and subsidizing the Bosnian Serbs in their efforts to seize as much as possible of Bosnia. There are lengthy arguments on these points which I won't reprise here. The key point is that by early 1995, as the Bosnian war was entering its fourth year, most European governments were under heavy pressure from public opinion to do something about the conflict in Bosnia. The US government felt less pressure from public opinion, but the Clinton administration had come to realize that two years of attempted diplomacy had accomplished exactly nothing.

At that point the Bosnian Serbs were, very broadly speaking, winning the war. Although they were only about 35 to 40 percent of the population, they had managed to seize and control over half of Bosnia's land area. They had failed to take Sarajevo, but they had control of most of Bosnia's agriculture and industry. They were the most numerous single group, after all, and they were also strongly supported by Serbia, which gave them arms, supplies, and financial and logistical support. So they had no compelling reason to stop fighting. By the summer of 1995 they were threatening some of the "safe areas" that had been set up for Bosniak refugees. Given their track record, there was a reasonable fear that this could lead to another round of ethnic cleansing and massacres.

So NATO decided to intervene. In August 1995, NATO launched Operation Deliberate Force, a series of air strikes against the Bosnian Serb military. Operation Deliberate Force has been mostly forgotten, but it was this -- not the Kosovo conflict a few years later -- that was the first intervention by NATO in the former Yugoslavia. (Indeed, I believe it was the first significant use of offensive force by NATO anywhere, ever.)

Operation Deliberate Force was a pretty complete success. The Bosnian Serbs couldn't continue their offensive against opponents backed by NATO airpower; indeed, it soon became clear that they would be forced back and would lose ground. They appealed to Milosevic for more assistance. But Milosevic had no interest in spending more money and effort to support the Bosnian Serbs in an impossible fight against NATO. After all, they had already achieved their major war goals: they had seized half of Bosnia, driven out almost all of the non-Serb populations, and set up an effectively independent government. Capturing Sarajevo would be nice but was hardly necessary; the Republika Srpska was already a going concern. So, Milosevic refused any further help.

Meanwhile, there were two additional factors in play: Croatia and the Bosnian Croats. In August 1995 the Croatian army launched the extremely successful Operation Storm, wiping the breakaway "Republic of Serb Krajina" off the map in less than a week. Operation Storm had been prepared long in advance, with tacit technical and logistical support from several NATO members. Nevertheless, the Croatian army achieved complete strategic and tactical surprise. The Serb parastate collapsed and over 100,000 ethnic Serb refugees fled into Serbian Bosnia and Serbia itself.

Then just a few weeks later, in September, the Bosnian Croats inside Bosnia launched Operation Mistral. While much smaller than Operation Storm (the Bosnian Croats were much fewer in number and less well equipped than the Croatian army), Operation Mistral was also a modest success; the Bosnian Croats seized several towns that had been held by the Bosnian Serbs. From a Serb POV, this raised the possibility of Bosnian Croat and Bosniak ground troops moving forward with the direct support of NATO airpower -- or, even more alarming, the possibility of direct intervention by the newly invigorated Croatian army on the ground in Bosnia.

The Bosnian Serbs had some modest air defenses: they did manage to shoot down one or two NATO planes. But they really had nothing that could counter the multiple threat of NATO bombing, Croat/Bosniak attacks under NATO air cover, and the possibility of intervention by the Croatian army. So, almost overnight, the Serbs went from pushing forward and winning the war to falling backwards and losing the war. Also, they now had the alarming fate of the "Republic of Serb Krajina" in front of them: their brother ethnic Serb parastate had been wiped right out of existence in a week. Their only options now were to beg for help from Milosevic in Belgrade -- and, if he refused, to quickly negotiate a deal before they lost even more ground.

So when Milosevic refused to help, that forced the Bosnian Serbs to accept a cease-fire and, ultimately, a negotiated peace. The bombing started in August 1995; it ended less than a month later, in September, with a cease-fire. By December 1995 a peace treaty had been signed, the famous Dayton Accords. The Accords have been heavily criticized, then and since -- but they ended the war, full stop.

So Operation Deliberate Force was a success by any standard. Unfortunately, the nature of that success was misunderstood. European political and military leaders saw that after three and a half years of bloodshed, ethnic cleansing, and massacre, a firm stand and three weeks of bombing had solved the problem, or anyway had at least ended the war. This gave everyone the idea that problems in the former Yugoslavia could be solved by a quick bombing campaign. When confronted with the power of NATO, the Bosnian Serbs had quickly backed down. So, if confronted with similar overwhelming force in Kosovo, Milosevic and Serbia would probably back down in much the same way.

There were two problems with this analysis. The first problem was that while Milosevic didn't care that much about Bosnia, he cared very much about Kosovo. In Bosnia, it was a question of whether ethnic Serbs would control 52% or 49% of the country, and whether they would have complete de facto independence or whether they might have to give insincere lip service to a very weak Bosnian central government. From Milosevic's POV, these issues were pretty secondary -- almost trivial, really. He had most of what he wanted in Bosnia: a large "ethnically clean" Serbian buffer state along his western border, beholden to him and his government and effectively controlled by Belgrade. The precise details of that state's borders and authority were minor and negotiable.

But Kosovo, on the other hand, was existential. Serb rule over Kosovo was a core interest to multiple actors -- the Serbian public generally, Milosevic's party and supporters particularly, and Milosevic himself. Milosevic could let his Bosnian Serb clients give up some scraps of land in Bosnia and accept the nominal sovereignty of a toothless Bosnian government. That was really no big deal. But losing Kosovo? That, he could not afford and would not accept.

The second problem was that Europe's leadership forgot that Operation Deliberate Force was just one part of a three-pronged strategy. It happened alongside Operation Mistral (offensive by Bosnian Croats, boots on the ground inside Bosnia) and Operation Storm (highly successful offensive by Croatian army, threatened massive invasion by ground forces). In Kosovo, one of those prongs (threat of invasion) would be completely absent, while another (local combatants in theater) would be much weaker. So while in 1995 in Bosnia, the Serbs had folded quickly in the face of a brief air campaign, in 1999 in Kosovo, things would be rather different.

Okay, I will pause here and see if this is acceptable to the mods.

Okay, so we've talked about Bosnia and how that set things up for Kosovo. Now, what happened in Kosovo that made NATO want to get involved there?

Under Yugoslavia, Kosovo was a "special autonomous province" of Serbia. This meant that it had limited self-rule. Since the majority of Kosovars were ethnic Albanians, this means that under Communist Yugoslavia, Kosovo's politics and its economy came to be dominated by Albanians. The Serbs -- who were a majority in Serbia as a whole, but a minority in Kosovo -- came to resent this.

The situation got steadily worse through the 1970s and 1980s, because the Albanian majority kept growing. In broad numbers, in the years after WWII Kosovo was about 70% Albanian, 25% Serbs, and 5% others. By the 1980s those numbers were more like 80% Albanian, 15% Serbs, and 5% others. Partly this was because the socially conservative Albanians had larger families; partly it was because of differential emigration, with Serbs easily able to move to Serbia proper in search of better jobs and opportunities, while Albanians were more likely to stay in Kosovo. In any event, as the Serbs within Kosovo became more outnumbered, Kosovo became more and more of a rallying cry for Serb nationalism. This all came to a head in 1989, when Serbia revoked Kosovo's autonomous status and took over direct rule from Belgrade.

Milosevic's government was generally corrupt and kleptocratic. However, for Albanians in Kosovo, it was also brutally oppressive. Albanians were dismissed from almost all management positions in state-owned enterprises (which is to say, almost all important enterprises) and replaced with Serbs. Albanians were completely purged from the police, the judiciary, and the upper ranks of the civil service. The University of Pristina, which had been the center of Kosovar Albanian intellectual society, was turned into a Serbian university, with Serbian professors, administrators, and students replacing the Albanians. All major media were under Serbian control; protests and strikes were brutally suppressed.

I'll pause here and note that, then and later, some observers tried to present this as a "clash of civilizations" between Christian Orthodox Serbs and Muslim Albanians. This was, by and large, nonsense. While religion made a comeback in post-Communist Serbia just as it did everywhere else in the Communist world, it wasn't a significant driver of the Kosovo conflict. Neither group was particularly religious. Even at the time, a common joke was that "Kosovo is a fight between people who never go to church on Sunday and people who never go to mosque on Friday". It's also worth noting that about 5% of Kosovar Albanians were Catholic, not Muslim. It made no difference; the Serbs treated them exactly the same. It was an ethnic conflict, not a religious one.

Bad as things were for the Kosovar Albanians, for the first few years -- from 1989 to 1995 -- they could have been much worse. There was no war. The Serb police were notoriously brutal and corrupt, ordinary citizens were subject to arbitrary arrest and harassment, and troublemakers were likely to be beaten or tortured, but there were no mass murders or massacres. The Albanians saw mass unemployment and dramatically decreased access to health care and basic services, but there wasn't mass famine. Albanians were mostly locked out of higher education, elected office, and the civil service, but nobody was being ethnically cleansed.

Through this period, the Albanians mostly relied on peaceful and non-violent resistance, under the leadership of Ibrahim Rugova. Rugova is a controversial character, but he probably delayed the eventual spiral of resistance -> violent oppression -> more violent resistance by several years. Whether this was ultimately a good thing... well, as I said, he's controversial. But anyway, from 1989 to 1995 Kosovo was miserable and oppressed, but relatively peaceful.

After 1995 things began to change. The first big change was of course the Dayton agreement itself. Dayton solved the problem of the war in Bosnia -- but it completely ignored Kosovo. The Kosovar Albanians felt, not unreasonably, that they'd been ignored and abandoned by the West. Rugova's prestige took a hit; nonviolent resistance had accomplished nothing. Voices favoring more violent methods began to be heard. In 1996, the embryonic Kosovo Liberation Army made its first moves, with a handful of attacks on Serb policemen and particularly oppressive and unpopular Serb officials. These attacks were not particularly well planned or coordinated, but they alarmed the Serbs and provoked a crackdown -- which of course gave the KLA even more credibility with ordinary Albanians.

A second driver of violence came in 1997 when the government of Albania, just over the border, collapsed. Albanian was thrown into complete anarchy for several weeks. During this period, the local armories were all looted. Albania was full of these armories, because the Communist dictator Enver Hoxha had believed that in the event of invasion, the people would need to be armed quickly. When they were looted, tens of thousands of weapons suddenly came available -- rifles, pistols, submachine guns and light machine guns, grenades. For a while, you could walk into any village market in rural northern Albania and buy grenades for a dollar apiece, a pistol for ten dollars or a rifle for twenty. Since the border between Albania and Kosovo was fairly porous, thousands of Kosovars did just that. Suddenly Kosovo was awash in guns.

So the security situation in Kosovo began to slide rapidly downhill. The Serbs became more paranoid and oppressive; human rights violations got worse; the economy slumped; and the Albanians became ever more resentful and more inclined to ignore Rugova and support violent action against Serb rule. But up to the spring of 1998, two and a half years after Dayton, Kosovo still was /relatively/ peaceful. And -- up until the spring of 1998 -- the rest of the world wasn't really paying much attention to Kosovo.

And then in early 1998 the Serbs decided to eliminate a local KLA leader named Adem Jasheri.

[Pause again to confirm this is OK with the mods.]

So, Adem Jashari. Very short version: he was a guerrilla leader / local strong man in a region of Kosovo that was already challenging for the Serb authorities -- 100% ethnic Albanian, rugged terrain. And in March 1998, the Serbs decided to make an example of him. They came into his village with hundreds of troops, surrounded his house, and just killed everyone. They ended up killing about 60 people: Jasheri, almost his entire extended family, some of his guerrilla comrades, and some unlucky people who just happened to be there.

This was intended as a show of force. It backfired spectacularly. Kosovar Albanian society was socially conservative and extremely family-oriented, so the idea of wiping out an entire extended family was utterly horrific. Also, say what you like about Jasheri, he and his group went out heroically -- surrounded, guns blazing, fighting to the last. So Jasheri became an instant martyr, and his death became the incident that flipped Kosovar Albanian society from unhappy and restive to full-blown rebellion. The Serbs didn't realize it at the time, but they'd flipped a lit match right into a pool of gasoline.

(I'll pause here to note that officially the government in Belgrade was still "Yugoslavia". Formally, Yugoslavia wasn't dissolved until 2003. However, in reality Yugoslavia had disappeared years ago; from 1989 onwards, state authority in Kosovo was entirely Serbian. So, saying "the Serbs" is simply more accurate, even if it's not formally correct.)

From the death of Adem Jasheri to to the beginning of the NATO bombing was almost exactly one year, from March 1998 to March 1999. And during this year, the Serbs suddenly found themselves confronting a full-blast guerrilla war in Kosovo, firmly supported by the majority ethnic Albanian population. Occasional shots fired at Serb policemen escalated into guerrilla squads coming after police stations with machine guns and mortars. Bomb attacks became commonplace. Symbols of Serbian authority -- courthouses, government offices -- became targets. Ordinary Serb civilians no longer dared mingle with Albanians, and withdrew into their separate villages and neighborhoods.

The Milosevic regime responded with more oppression and more violence. More Albanians were fired from their jobs. A state of emergency was declared; the army moved in; the police were reinforced with the "anti-terrorist unit", which was already notorious for its brutality. Curfews were declared and aggressively enforced, though only against Albanians. Where previously troublemakers might get a beating or lose their job, now they simply disappeared.

Mass killings and massacres now began to appear: Ljubenic, Gornje Obrinje, the Panda Cafe shooting, the village of Racak. Most of these were on a relatively small scale compared to Bosnia -- five people here, a dozen over there, about forty in Racak -- but the trend was steadily towards more and larger scale violence. By the spring of 1999, large areas of Kosovo were "no-go" regions, where Serbs could not venture without large parties of armed men. As rural areas became free-fire zones between the Serb military and the KLA, over 100,000 Albanians fled their homes, some fleeing into the towns, others over the borders to Albania and Macedonia.

It's during this period that the rest of the world, especially Europe and the US, began to be strongly interested. Kosovo in 1998 was all too reminiscent of Bosnia several years earlier. It was entirely reasonable to assume that before long, the Serbs would escalate to ethnic cleansing (as they had almost everywhere else -- the Serb parastates in Croatia, the Republika Srpska in Bosnia) and to large-scale massacres (as they had in Bosnia). So, the West began to put pressure on Milosevic to back off and to negotiate a deal with the Albanians.

Unfortunately, this wasn't something Milosevic could really do. He had originally come to power on a wave of Serb nationalism driven by the "oppression" of Serbs in Kosovo. Serb dominance in Kosovo was his signature achievement. Realistically, there was no long-term solution in Kosovo without relaxing the oppression admitting the Albanians back into partnership in government. However, since the Albanians outnumbered the Serbs five or six to one, it was very hard to see how this could be implemented without effectively conceding control to the Albanians -- and this, no Serb government could accept. Also, while some sort of moderated power-sharing with protections for the Serb minority might have been possible years ago, by 1999 it was probably no longer realistic. The Albanians, enraged by years of plunder and oppression, were in no mood for peaceful coexistence. The Serbs of Kosovo, looking around, could easily guess their fate under a vengeful Albanian government. Neither side could imagine trusting the other.

Furthermore, official Serb policy for years had been that Kosovo under Serb rule was /better/ -- more prosperous, more peaceful. Most Albanians were happy, ran the official line. Only a few separatists (who were also gangsters and drug dealers, and possibly jihadis as well) were causing the problems.

Of course this was nonsense and everyone knew it. Nevertheless, after years of demonizing the KLA as bloody-handed murderers, it was almost impossible for the Serbs to recognize and negotiate with them. For a rough analogy, consider how long it took the UK government to reluctantly acknowledge that it needed to sit down and talk to the Provisional IRA. It took nearly 20 years -- and the IRA and the British were less far apart than Milosevic and the KLA.

So, the Milosevic government was extremely reluctant to even acknowledge or talk to the KLA, and also had zero desire to make any sort of meaningful concessions to the ethnic Albanians. On the international stage, they took a stand of pure sovereignty, insisting that whatever happened in Kosovo was a purely internal "Yugoslav" affair. If the Belgrade government had to take strong measures against gangsters and terrorists, that was no business of any other state.

(The Serbs did still recognize Ibrahim Rugova as an Albanian leader they could talk to. Unfortunately by this point, Rugova was almost powerless; he was trying to promote nonviolent resistance, and not many Albanians were listening any more. And even Rugova insisted on a transition to majority rule, meaning Albanian rule, which was unacceptable to Belgrade.)

-- I'll pause here and note that I'm simplifying a very complicated story. There were cross-currents on both sides; the KLA weren't angels; there was internal Serb resistance against Milosevic; "the West" was hardly a monolith. But this narrative is already thousands of words long, and I'm not even sure I'll find time to finish it.

Anyway, questions and comments (about Kosovo, and nothing more recent than the last 20 years) are welcome.

Final installment.

So, by early 1999 various attempts to resolve the Kosovo situation had failed. In autumn 1998 the Americans had sent Richard Holbrooke as a special envoy to Belgrade. Holbrooke negotiated a deal that looked good on paper, with a ceasefire, partial Serb withdrawal, international observers, and negotiations leading to eventual elections. However, in practice the KLA ignored the deal – they hadn’t been consulted, after all – and the Serbs quickly began to foot-drag and renege. So, by January 1999, armed intervention was under serious discussion.

One theory of the conflict deserves mention here. This is the idea that US President Bill Clinton provoked the bombing campaign in order to distract public attention away from the Monica Lewinsky scandal and his subsequent impeachment. This idea was widely discussed at the time and was popularized by the movie Wag the Dog.

It’s not completely impossible! But on the other hand, it’s not really provable. There’s no way to know what Clinton was thinking. Also, there are several problems with this theory. One is that, in the particular case of Kosovo, the Americans were not the ones pushing hardest for action. American public opinion was slow to become interested in Kosovo. It was in Europe that reports of oppressions and atrocities circulated most widely. “Tabloid headlines in London, above the fold in Berlin, page three in Washington”. Britain’s Tony Blair, in particular, was out ahead of Clinton; he was a passionate advocate for intervention from quite early on.

Another problem with the theory is that Clinton wasn’t even the biggest hawk within his own administration. That honor probably belongs to his Secretary of State, Madeline Allbright. Allbright had several bad experiences with Milosevic and neither liked nor trusted him. But there were plenty of other voices within the administration urging a hard line.

Anyway, I mention the “Wag the Dog” theory because it’s still out there and sometimes comes up in online conversation. Okay, back to Kosovo.

The particular status of Slobodan Milosevic deserves some mention here. Milosevic had never been popular in Europe; rightly or wrongly, he was seen as the most culpable actor in the wars in Croatia and Bosnia. However, after Dayton there was a hope that he might now become a force for stability in the region. These hopes were disappointed. Not only did repression in Kosovo continue and worsen, but Belgrade continued to support the Bosnian Serbs in their endless conflicts with Bosnia’s weak central government. From Milosevic’s POV, he was maintaining a valuable buffer on his border; from a European perspective, he was continuing to meddle and spoil, preventing Bosnia from emerging as a viable state. (To be fair to Milosevic, it turned out that almost every other Serbian government would take a similar position. But this was not apparent at the time.) More generally, Milosevic’s Serbia continued to be a corrupt kleptocracy with close ties to organized crime, and generally had poor to terrible relations with its neighbors in the region and with the rest of Europe generally. So, by 1999, both European leaders and European public opinion were quite thoroughly sick of Milosevic, and open to the idea of an intervention that might remove or at least neutralize him.

It should be noted here that Milosevic was not actually a dictator. His party and his allies controlled most Serbian media; they dispensed immense amounts of patronage; the judiciary was under their control; opposition leaders were spied upon, slandered, and harassed; and protestors or whistleblowers were likely to be targeted by nationalist paramilitary groups or organized crime with close ties to the government. Nevertheless, Serbia was not a one-party state. There were regular elections, and Milosevic had to contest these. Also, Belgrade in particular had a history of anti-government protest going back decades; even under Communism, protests and riots in Belgrade were a concern for Yugoslav governments. (And, in fact, it would be Belgrade protestors who would eventually bring Milosevic down.) So, Milosevic was hardly a Hitler or a Saddam Hussein. He had to worry about public opinion, and also about keeping the loyalty of the army, the security services, and Serbia’s oligarch class.

On one hand, this narrowed Milosevic’s room for maneuver. Serb domination in Kosovo was popular even with most of the opposition. Among Milosevic’s core supporters, it was absolutely non-negotiable. A real dictator might have been able to ignore these sentiments; Milosevic could not.

At the same time, it made him more vulnerable. A defeat in Kosovo would certainly weaken and discredit Milosevic, and might well lead to his overthrow. (As in fact it did, though it took more than a year.) So, while almost nobody was openly talking about regime change in Serbia -- bad form while you're actually in the middle of diplomatic negotiations with a regime -- it was absolutely on the menu.

Okay, so all this brings us back to your original question: “Why did the NATO countries care about Yugoslavia?” – or, a bit more broadly, why did the Kosovo War happen?

I think we can sum this up as follows. The main drivers for NATO intervention were (1) Fear of “another Bosnia” in Kosovo – another Balkan war, with massacres, refugees, and ethnic cleansing; and (2) European public opinion, which put increasing pressure on European leaders to intervene, and (3) a belief that Milosevic was the problem, and thus a desire to humiliate or break him, hopefully leading to his overthrow or at least eliminating him as a problem going forward.

In addition, three other factors made the intervention easier. These weren’t things that pushed NATO forward, but they made intervention seem simpler, more tempting, and more reasonable. These were (1) the experience of Bosnia; (2) the diplomatic isolation of Serbia, and (3) the weakness of Russia.

The experience of Bosnia has already been discussed. In brief, a short NATO bombing campaign in 1995 brought the Bosnian Serbs to the negotiating table and led directly to the Dayton Accords and the end of the war. There was a widespread belief that a bombing campaign in Kosovo would follow the same pattern – in short, that the Serbs would quickly fold.

The diplomatic isolation of Serbia under Milosevic is not much discussed, but it was absolutely a factor. Simply put, Milosevic had no allies in the region. Croatia, Albania and Hungary were hostile. Romania and Bulgaria had just joined NATO. Macedonia’s government felt – reasonably enough – that Milosevic was ignoring their security concerns, since Macedonia also had a large Albanian minority who were very engaged with events in Kosovo. Even Montenegro, which was still nominally joined with Serbia in Yugoslavia, had no interest in maintaining Serb domination in Kosovo; the Montenegrin government stood aloof from Milosevic, and would be effectively neutral in the war. The only country in the region that was somewhat friendly to Serbia was Greece. But while Greek public opinion was sympathetic to Serbia, the Greek government was not about to throw Milosevic a lifeline; they might worry about Albanian irredentism in northern Greece, but they didn’t like or trust Milosevic either. So, an attack on Serbia would not (it was thought) drag NATO in any other conflicts, nor would any of his neighbors give him help that would prolong the conflict.

Finally, the weakness of Russia absolutely allowed NATO to be much less cautious. Russia had traditionally been the great power protector of Serbia, and this relationship had to some extent been revived in the 1990s. However, in 1999, Russia under Yeltsin was near a nadir of international influence and prestige. It was of course still a nuclear power; but Russia had no allies worth mentioning, the Russian economy was in shambles, and the Russian military had suffered a humiliating defeat in the First Chechen War. NATO planners did not believe that Yeltsin’s Russia had either the will or the capacity to intervene in Kosovo. In this they were mostly correct; Russia gave moral and diplomatic support to Belgrade, and staged a dramatic last-minute intervention at Pristina Airport, but in the end it made no difference. So, to summarize, NATO intervened to prevent “another Bosnia”; because public opinion, especially in Europe, was putting pressure on leaders; and because of a belief that Milosevic was the problem, and a desire to see him weakened or removed. The intervention was made more attractive by the experience of Operation Deliberate Force three years earlier; by Serbia’s diplomatic isolation; and by perceived Russian weakness.

Okay, I hope this answers your questions as to why the Kosovo War happened. The details of what happened are perhaps a story for another thread. Cheers!