Soft power and the institutions of the west are a big part of the US power projection that prevents war. Those countries are very lightly militarized (<2% of GDP on military), and it's because they are under US protection not because they are democracies.

Yugoslavia was basically outside the US sphere or influence, and it was a regional conflict(not of vital importance) so the actions by the US were more limited. Also that's a weird example to bring up in support of Democratic peace theory as "Bosnia, Croatia, Slovenia, Serbia, Montenegro and the Serb Autonomous Regions were all formal multiparty democracies" [1]

[1]https://en.wikipedia.org/wiki/List_of_wars_between_democraci...

"Formal" does quite a lot of heavy lifting there.

Within the community of formally democratic countries, countries that democratized only very recently (last 10 years of their existence or so) form a very specific sub-club. Some of those might be autocracies by other name, some others too chaotic to be even a -cracy.

It takes some time, I would say, at least three or four full election cycles with peaceful transfer of power, before a people learns to be a democracy.