Calling it the Soviet-Afghan War is quite misleading indeed, and is no doubt a post-Cold War invention. The Soviets initially intervened for humanitarian reasons on the side of the government, believing that the Communist General Secretary Hafizullah Amin was an evil dictator, especially after he murdered the previous General Secretary Taraki, who the Soviets very much preferred. They were right, Amin executed something like 40,000 people in just one year, and while Muslim anti-Communist uprisings began under Taraki, they were intensified by Amin's wanton brutality. Spetsnaz dropped in, assassinated him, and replaced him with the much more liberal Karmal.

Afghanistan had immense strategic importance to be sure. It bordered the Soviet Union, threatened Pakistan a key American ally, and its porous borders threatened the stability of places like Tajikistan and Uzbekistan. It also held great mineral wealth and a large population. On top of that, it had become Communist through a home-grown popular revolution, and if successful, was believed to be a good model for further revolutions in the Islamic world, particularly when challenged by Iran, which had just had its own Islamic Revolution.

More importantly, the mujahideen were the very definition of the Communist class enemy. They were comprised primarily from local Pashtun nobility, wealthy bourgeoisie, clergy, or members of the intelligentsia, who rallied young men chiefly through rhetoric attacking the progressive Communist policies, especially those on women. In 1979, they seemed like the petty comebacks of a disgruntled conservative group of men who resisted the inevitable modern advance of Socialism. It was not expected that the Soviets would have to do much fighting, initially believing that they would primarily be securing the cities and supply lines, freeing the Afghan Army to mop up the rebels, and it was further expected that the largely peasant population would embrace Socialism.

Owing to American funding and influence, the Mujahideen were soon extremely well-armed and well-versed in guerilla tactics. More importantly, the Americans trained the Mujahideen propaganda campaign, flooding Afghanistan with Deobandi material that very rapidly radicalised what had been a moderate country of Hanafi Islam. This defeated the Soviet aim of flipping the peasant population, which had now turned to the religious leaders, who were also dramatically weakening the Afghan army and encouraging mass desertions. It took a lot longer before the Soviets realised that Socialism and any other progressive cause was effectively powerless.

There is strong evidence that Brezhnev never wanted to be involved in Afghanistan to this scale, calling it a "dirty, dusty place, with no value to us". It is likely that Soviet forces on the ground were unable to fulfill their missions due to ineffective Afghan forces, and so the Afghan government requested more Soviet forces. But each Soviet soldier in the country only increased resentment against the Soviets, reducing the effectiveness of the Afghan army. And so the vicious cycle was started.