Why was the Balkan region referred to as the "Powder Keg of Europe" prior to World War I?

The powder keg of Europe also commonly known as the Balkan powder keg was the name given to Balkans. This was in the 20th century before there was World War 1. This Balkan keg consisted of many Balkan states together, originally from Austria-Hungary. The combined states were called the powder keg of Europe in order emphasize unity.

This is because at the time, nationalistic and imperialistic rivalries were increasing and the Balkan region needed to unify in their attempt to portray themselves as a powerful nation. It didn’t have anything to do with the Yugoslavia invasion. Or any disruption of power by the Ottoman Empire.