Its a reference to how the balkan peninsula, specifically former yugoslavia, was broken into a multitude of weaker independant states primarily by exploiting ethnic tensions. This allowed western capital to exert significant influence on the political-economy of these countries in a way they could not when they were united. As these new states fought eachother and destroyed themselves foreign capitalist bought up their economies and to this day remain significant employers in the region; allowing them to extract wealth they couldn’t have without balkanization and the violence that came with it.

It essentially boils down to the divide and conquer strategy. I honestly don’t believe the west is currently capable of accomplishing this in Russia no matter the outcome of the Ukraine war. The Balkans have a history of nationalist movements and a dense diversity of cultures that made them much more vulnerable to this strategy than modern Russia would be.