The Second Balkan war was a catastrophic blow to Russian policies in the Balkans, which for centuries had focused on access to the "warm seas". First, it marked the end of the Balkan League, a vital arm of the Russian system of defense against Austria-Hungary. Second, the clearly pro-Serbian position Russia had been forced to take in the conflict, mainly due to the disagreements over land partitioning between Serbia and Bulgaria, caused a permanent break-up between the two countries. Accordingly, Bulgaria reverted its policy to one closer to the Central Powers' understanding over an anti-Serbian front, due to its new national aspirations, now expressed mainly against Serbia. As a result, Serbia was isolated militarily against its rival Austria-Hungary, a development that eventually doomed Serbia in the coming war a year later. But, most damaging, the new situation effectively trapped Russian foreign policy: After 1913, Russia could not afford losing its last ally in this crucial area and thus had no alternatives but to unconditionally support Serbia when the crisis between Serbia and Austria broke out in 1914. This was a position that inevitably drew her, although unwillingly, into a World War with devastating results for her, since she was less prepared (both militarily and socially) for that event than any other Great Power.