Why was the Balkan region referred to as the “powder keg” of Europe prior to world war 1?

A. Nationalistic and imperialistic rivalries were increasing which caused stress with the alliance systems that many of the Balkan nations were members.

B. The aggression of the Ottoman Empire was disrupting the balance of power.

C. The area was the leading supplier of military equipment to the rest of the world.

D. Yugoslavia was invading its neighboring countries.