Around 1906 the Balkans again became the focus of great-power rivalry, as Russia renewed its interest in the Balkans and became Serbia's great-power patron. A crisis erupted in 1908, when Turkey began to be reorganized as a constitutional state. Bosnia and Hercegovina, which was Turkish territory under Austro-Hungarian administration, was invited to send delegates to the new Turkish parliament. Austria-Hungary responded by formally annexing Bosnia and Hercegovina in violation of various international agreements. It quelled Turkey's objections with financial compensation. But by alienating Russia and Italy, the annexation was a costly diplomatic victory for Austria-Hungary at a time when the military alliance system of Europe was moving against it. Britain had resolved colonial rivalries with both France and Russia, paving the way for the cooperation of the three countries in the Triple Entente.

Following the crisis over Bosnia and Hercegovina, Russia encouraged the independent Balkan states to form what was intended to be an anti-Austro-Hungarian coalition. But the new coalition, called the Balkan League, was more interested in partitioning the remaining Turkish territories in the Balkans, and it defeated Turkey in the First Balkan War in 1912. The Balkan allies turned on each other in 1913 in a war over the division of the former Turkish territories. In this Second Balkan War, Serbia doubled both its territory and its population.

Data as of December 1993