Dear Kaze,
Your third point illustrates the Balkans.
Turkey had converted some south Slavs to Islam (Bosniacs and Kosovars) and used them to guard the western border of the Ottoman Empire.
The Austrian-Hungarian Empire converted some south Slavs to Roman Catholicism (Croats) and used them to guard the eastern border.
Russia had converted some south Slavs to Eastern Orthodox Catholicism (Serbs) and used to guard the southern border.
Throw in a few un-related tribes like Hungarians (unique language), Bulgars, Romanians (dialect of old Latin), etc. and you get many small groups willing to fight each other over small pieces of land. Both tribes may have retained historical claims on various pieces of land, but those lines blurred over centuries of migrations, politics, royal marriages and wars.
Meanwhile, large, wealthy countries are becoming more stable, more urbanized and less violent. Certainly the last thing Britain wanted was a European War.
Sadly, small Balkan tribes dragged large empires down to their level and ground them into dust!