By the turn of the century, Europe was largely destabilized by its own system of alliances. Germany and the Austro-Hungarian Empire formed one such alliance, known as the Central Powers, while France, Russia and Great Britain formed another alliance to meet this threat. The whole system began to topple with the assassination of the Archduke Francis Ferdinand on June 28th 1914, while visiting Serbia. The Austrians were outraged by this assassination of the heir to their throne.
On July 28, 1914, Austria- Hungary declared war on Serbia. Because of the alliance system the other powers were rapidly drawn in, and by August 4 most of Europe was at war.