Napoleon's diplomatic efforts are often not looked into since we have an image of him in the West as a warmonger and would-be invader/conquerer. The truth is, all of the three wars that Napoleon started himself (Egypt 1799, Spain, 1807, Russia 1812), he lost. France either never had an adequate enough navy or an extended logistical port to which it could wage war across seas. This is why Napoleon ceased plans for an invasion of England in 1805, as he could not possibly defeat the Royal Navy and get across the English Channel.

Now, let's get to his diplomacy. France in 1792 was a revolutionary state and the rest of Europe was the old order of monarchy houses (Hohenzollern, Windsor, Hapsburg, Romanov). These dynasties were directly threatened if France won, hence they waged war constantly against France, in order to quell the revolution there. France, from 1792-1800, was constantly at war. Only after Napoleon's continued success against Austria and other French heroics does peace come, in 1802 with the Peace of Amiens. But, this like the Treaty of Versailles, is only an armistice.

England, unlike Austria, Prussia, and Russia, has the finance and security to continue the war against France. Since Napoleon rose to power on the back of his military success, a military defeat will oust him. So, they finance Austria, Russia, and Prussia to wage war again. Except, France and Napoleon win again. He, desiring peace, makes it with Russia in the Tilsit Treaty. He proposes that since England is the main cause of the continued conflict and he cannot invade it, he must weaken it enough economically so that they will come to the peace table and negotiate. He creates the Continental System, imposing a blockade on trade with England. This is why he never annexes Austria or Prussia, as this would upset the Tzar of Russia.

The Tzar, came to power after his own father was assassinated by his court officials, with the approval of the British ambassador to Russia, after he made peace with France and attempted to institute an anti-corruption campaign (1801). Tzar Alexander I never punishes his father's murderers and realizes he cannot make peace with France and it is only after two humiliating military defeats that he accedes to even negotiate with Napoleon. Meanwhile, Napoleon realizes that Portugal is trading with England, against his Continental System. He invades it but then invades Spain also. This leads to the Peninsular War (1807-1814) since most of Spain rejects French Revolutionary ideas as they are against the teachings of the Catholic Church (much like the Spanish Civil War of 1936-39). Meanwhile, just as Napoleon is about to completely subjugate Spain, Austria declares war on France. It is defeated and Napoleon, after defeating it successfully the fourth time, rightfully imposes harsher peace terms but still does not annex out of respect for the Tzar.

Meanwhile, the Tzar's clock is ticking. His economy is weakened due to the Continental System and he knows that peace with Napoleon is unpopular at home, both with the nobility (who deem it a threat against their power) and the peasantry (who deem Napoleon and his French Revolution, the Anti-Christ and his teachings). He refuses to negotiate with Napoleon, even after the latter implores repeatedly to at least come to the negotiating table to avoid war. Despite claims to the contrary, Napoleon knew the horror of wars with Russia since they caused his Grand Armee the most casualties. But Tzar Alexander does not budge and knows war is essential for the Romanovs. Napoleon is faced with two choices. Either he can liberate Poland (which will offend the Tzar) or invade Russia for a quick victory in the hopes that the Tzar sues for peace. He wants to please the Tzar, so he opts for a quick battle. He remains in Moscow since he hopes that the Tzar will come to negotiate. But he does not and Napoleon's Grand Armee is destroyed.

Prussia and Austria, become emboldened seeing Napoleon weakened, breaking their treaties and Emperor Joseph even wages war against his daughter and grandson, Marie Lousie and Napoleon II. Napoleon loses since the peace terms offered are to return France's borders to 1792, which would undo all the work of France for the past 22 years. Napoleon states that he cannot accept these terms since the royal houses can lose 100 battles and retain their thrones. However, if he loses even one, he will be finished. Which proves correct. Even after his return from Elba, he offers peace to all the royal houses but they want no semblance of revolution and instead opt to wage war against France, for the 7th time. They do not execute Napoleon as that would send the message that regicide is appropriate to the masses.

So, it is not so much that Napoleon was terrible at diplomacy, as much that the two forces and orders (revolution and reactionary) could not co-exist for an extended period of time. This was Kissinger's Ph.D. thesis when he uses the analogy for the Cold War, where we see again, that the side with the economic dynamism and strength, wins in the long-term against a military powerhouse (Athens and Sparta, pretty much).

The answer is more complicated. Yes, he was not adroit or successful at diplomacy but it hard to find many person in the era that would be much more successful at keeping the peace. He was highly responsible for the conflicts, nonetheless, and I would laid out his role in the wars at the later paragraphs but let imagine the situation without using his name.

I. The Napoleonic Wars

The war of first coalition had been won by France, and they demand a harsh treaty on Austria in order to weaken it severely, knowing that it may only be an armistice. Later, the Republic of France is corrupted and hated. Austria and French emigre seeing a chance to restore the Bourbons and recover the loss of the previous war, declared another war. A coup happened and a general took over the government. Soon after, the republic were saved and the general crowned himself emperor. At the time, they established client states in Italy and Germany occupied by French armies and ruled by French generals.

France was still in conflict with Britain. Britain did not have enough capability to defeat France and so seeking allies across Europe. The Russian ruler had a vision to end the revolution and Austria, which lost land, people and heritages in the previous war, still wanted to fight, they simply do not have enough money to do so. Britain can provide that. Meanwhile, France had internal peace, economic developments and its armies are veteran and well-equipped. When the war declarations arrived, they were more-than ready and victorious.

After years of wars, they established alliance with Russia, and set up the continental systems to weaken their old foe and increase their own economy. Without English goods on continental Europe, the French industry boomed. However, the economic effects negatively other parts of Europe, especially since they already bore the brunt of the horror of wars. The French army on the march, lived off the lands of the common people, causing miseries, starvation and resentment. France also conscripted their able-bodied men for their army in many other wars. Meanwhile, France seeing opportunity to create a puppet state in Spain, backstabbed their allies, adding more fury. Austria got popular supports from their populace and see the French losing theirs, declared another war. A few years after, Russia and Britain finally get to talk in preparation. Another war continued.

This is a very shortened version that I omit many events to squeezed this in. As you can see, there were hostile feelings all across the nations. They felt threatened by each other and wars are constant. Everytime, it ended, the defeated prepared for the next one. So what was Napoleon to blame for?

II. Napoleon' s Rule

According to David Chandler (who greatly admired Napoleon) as an administrator, he centralized all the decision making into himself. The only first-rate men in government is Talleyrand and Fouche. According to a biography of Talleyrand, the emperor did not made use of Talleyrand' s advises and instead replace him with a yes man. Critics of the Continental System, the treatments of client-states and the treaties imposed on the defeated came even from his own family and allies. Since Napoleon were the head of the government, he was responsible in handling the situations and he rarely made an effort to bring peace.

In a biography of Bernadotte, in the peace following the War of the Second Coalition he reccomended the Napoleon to reduce the numbers of troops stationed in foreign territories in Germany and Italy to reduce tensions, but Napoleon refused saying that it was for defense. When Napoleon build up his army to prepare for war, the coalition also do the same. More tension increased as the general feeling is that wars are inevitable. Despite this, Napoleon can relied on his superior army and generals to win the war declared, therefore he did not seriously consider ways maintaining peace as a better alternative, at least, when he was winning.

Sidenote: an influential mathematician who developed Game Theory us convinced that a nuclear war is inevitable. MIT have used several mathematics models with probability and petitioned that the US must launched the first strike. Since the nuclear war had not yet happened, the inevitability of the war is overreaching. Napoleon also stated several times, that he simplified his thinking to the laws of probabilities. He saw wars are inevitable and often was the first to strike even if the with the exception of the Spanish and Russian campaign, the wars were declared on him.

In Sir Lawrence Freedman' s "On Strategy" and Clausiwitz' s "On War", the more creative and cunning strategies tend to come from the losers as the winners simply continued the strategies that brought them. Napoleon did bring peace, again and again, through superior military power. Even, after Russian campaign, Napoleon still choose to relied on military might rather than an alliance with Austria. The English and Austria, instead prefered coalition building, which Sir Lawrence (self-confessing that it may be due to his British bias) believed that it is the superior strategy.

To answer your question, peace are short and in-between, he chose wars because he often saw them as inevitable, was successful in them and prepared for them. Diplomacy that can bring peace such as the Congress of Vienna might not be what most people would think achievable, at least in most of the wars.

Sources:

David Chandler. "The Campaigns of Napoleon: History Greatest Soldier".

Sir Lawrence Freedman. "On Strategy".

John Gill. "Thunder on the Danube".

Suzanne Desan. " Living the French Revolution and the Age of Napoleon".

Robin Harris. " Talleyrand: Betrayer and Saviour of France".

Barton. "The Amazing Career of Bernnadotte".