Way back in 1878, some of the great European powers at the Congress of Berlin awarded to Austria-Hungary the right to occupy the Balkan provinces of Bosnia and Herzegovina. These were territories under the power of the Ottoman empire, but many saw the Turks’ assertions in the area as weak and malleable. Thus, many nations coveted the two provinces . . . in fact, Austria and Hungary had each wanted the provinces for their individual selves, not to be ruled under their dual monarchy. Yet beginning in 1878, Austria-Hungary took over practical administration of these provinces . . . in name and in law, however, they still belonged to the Ottoman Empire.
That changed on October 6, 1908, when the dual monarchy (Austria-Hungary) announced its annexation of the two provinces. Austro-Hungarian foreign minister Baron Aloys von Aerenthal decided on the move after considering the negligible risks: annexing the two provinces would probably anger both the Ottoman Empire, as well as Russia (who had strong sympathies with the Slavs in the region), but the Turks remained relatively weak, and Russia was still reeling from her defeat in the Russo-Japanese War (and internal revolution) of 1905.
More than anything else, however, the annexation had infuriated the next-door neighbor to Bosnia: Serbia. Like many powers in and around the Balkans, the Serbs had great ambitions of uniting entire ethnic regions (so called) under their own banner. Austria-Hungary’s annexation not only swallowed up an area into which Serbia instead might have expanded, but it also put Austria-Hungary right on the doorstep of Serbia . . . a threatening springboard in the event that the dual monarchy elected to attempt another expansion of its empire.
In January 1909, the chiefs of staff of Austria Hungary (Franz Conrad von Hotzendorff) and German (Helmuth von Moltke) met to discuss some of the possible ramifications of the annexation. Among other things, Moltke assured Conrad that if Austria-Hungary ever went to war with Serbia, even as the aggressor, Germany would not only support the dual monarchy, but she would fulfill her obligation as an ally even if it meant going to war with Russia and France as well.
It’s not hard to imagine that much of the groundwork for WWI had been set.