"I really think you're discounting how momentous a thing the Balkan wars were."
I think you're discounting the fact that the Balkan states had been independent since the crushing defeat of the Turks in 1878 - a situation you say created more stability than any time since Greek independence half a century earlier. The Turks, contrary to your claims, were not the rulers of the Balkans in 1912. They had decades earlier lost Romania, lost Bulgaria in all but name, lost Serbia, Montenegro, etc. The only province that remained was Macedonia. Serbia did not "double in size", it gained 25,000 sq km in territory, about the same as Bulgaria gained after the two wars. Considering Serbia did the bulk of the heavy fighting in the first Balkan war and defeated Bulgaria after the latter's duplicitous attack in 1913, this wasn't a bad deal at all.
"If the long Ottoman Balkans can now be entirely made up of nation-states, why not the absurd collection of lands ruled by the Habsburgs?"
I fail to see why the partition of Macedonia mattered in this regard. The Ottomans still controlled the bulk of the Middle East and the Caucasus. The Russians controlled Poland, Finland, the Baltics, etc. And you're forgetting the massive overseas territories controlled by the British and the French. The loss of Macedonia didn't overnight turn the Austrians into the only multinational Empire. Even if Serbia had managed to dislodge Bosnia from Austrian rule, they still controlled huge swaths of territory in Central and eastern Europe. And WWI demonstrated that Austria-Hungary was not under any kind of serious nationalist threat from within, as the Croats, Slavic Muslims, and Poles fought loyally for the empire against their Slavic brothers.
" I refer again to the Moroccan crisis, and also not to Samoa and, the crisis which lead to France ceding land added to Kamerun.
I said they were good about resolving colonial issues without resorting to war. And none of your examples contradicts that, in fact I think they largely buttress it.
Consider the only major great power war of note during this period (New Imperialism) was the Russo-Japanese war, in which the historically hostile French and British were allied to opposing sides, and the result was the Entente Cordiale. The British and French, the two major overseas powers, did everything they could to avoid conflict with one another during the scramble for overseas territories. This can be clearly seen with the resolution of the Fashoda crisis. And indeed the first Moroccan crisis can be seen in this light too, as the Europeans held an international conference to resolve the dispute peacefully.
Considering just how many overseas territories were taken in such a short period of time, it is rather miraculous that wars between the European states did not break out.