A European Powder Keg is a Codex Entry featured in Battlefield 1. It is unlocked upon starting the singleplayer campaign.
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EMPIRES & ALLIANCES - A EUROPEAN POWDER KEG[]
The two sides in the war were two alliances of empires. the Central Powers were the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, and Bulgaria. The Entente Powers, today often referred to as the Allies, were composed of many more nations and featured the British and Russian Empires; two of the three largest empires in World history, who ruled more than a third of the world between them.
Before the war, though, the alliances had been somewhat different. The Triple Alliance between German, Austria-Hungary, and Italy was counter-balanced by the Franco-Russian alliance, and most people believed that these alliances would prevent war. They were wrong.