Why were the Balkans known as the powder keg of Europe in the early 1900?

The tensions in the area were rather high, as there were two major conflicting powers (Austro-Hungary and Russia), were heavily involved in the conflict of the region. Austro-Hungary held power over Bosnia, which the Serbian nationalists claimed as part of their country. Russia sided with Serbia, promising to protect them in the event of war. Tensions rose, like a powder keg, just waiting for the spark that would ignite and bring about conflict.

The assassination of Archduke Franz Ferdinand and his wife Sophie was the event that led Austria to declare war. This led to a chain reaction of war declarations that began World War I, much like the devastating effects of a powder keg.