Why were the Balkans called the power keg of Europe

As is insinuated by the name "the powder keg of Europe," the Balkans were not the major issue at stake in the war, but were merely the catalyst that led to the conflagration. ... The powder keg "exploded" causing the First World War, which began with a conflict between imperial Austria-Hungary and Pan-Slavic Serbia.

Explanation:

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b) the confederacy had to pay all union war expenses.