Question

The “Powder Keg” in the Balkans refers to the

invasion of the region by outside forces.
political instability of the region.
efforts taken to ease tensions throughout the region.
large number of munitions factories built in the region.

Answer 1

political instability of the region — the Balkans were called Europe's "powder keg" because ethnic tensions and rivalries made the area likely to ignite a broader war.