On 28 June 1914, the heir to the throne of Austria-Hungary, the Archduke Franz Ferdinand of Austria, was assassinated by a Serbian nationalist. This caused a rapidly escalating July Crisis resulting in Austria-Hungary declaring war on Serbia, followed quickly by the entry of most European powers into the First World War. Two alliances faced off, the Central Powers (led by Germany) and the Triple Entente (led by Britain, France and Russia). In 1918 Germany tried to overwhelm the Allies on the Western Front, but failed. Instead the Allies began a successful counteroffensive and forced the Armistice of 11 November 1918 that resembled a surrender by the Central Powers. Irredentism—that is the demand for reunification of Hungarian peoples became a central theme of Hungarian politics and diplomacy.