Here’s how Dominic Lieven‘s The End of Tsarist Russia dissects Balkan politics in the years right before World War I:

Here Macedonia remained the key focus of instability.  The commitment of the new regime in Constantinople to centralization and Turkish nationalism made conflict in the province even sharper than before 1908… Within Macedonia, Muslims (mostly but by no means only Albanians), Greeks, and Slavs were often in conflict.  Grigorii Trubetskoy wrote that the great majority of Macedonian Slavs were currently neither truly Bulgarian nor truly Serbian.  Which direction their identity took would depend on whether the Bulgarian or Serbian government and intelligentsia came to control the region.  This gave an added twist to the rivalry of the regimes in Sofia and Belgrade.  All the governments in the region were nationalist through and through.  This was the source of their legitimacy and of most local politicians’ sense of their own personal identity.  Where governments did try to show statesmanship and moderation, however, they could rely on being denounced by wide sections of their country’s intelligentsia.  Worst of all, the officer corps of all states in the region were shot through with extreme and aggressive nationalist assumptions and loyalties.

On the surface, Lieven is solidly in the “realist” camp that traces war to conflicts of national self-interest.  (See also here and here).  Read closely, however, Lieven’s definition of “national self-interest” is so psychological – so intertwined with being a people – that objective interests count for almost nothing.  Russians didn’t fight World War I for Russia.  They fought World War I for Russianness