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Austria-Hungary
On July 28, 1914, one month to the day after Archduke Franz Ferdinand of Austria and his wife were killed by a Serbian nationalist in Sarajevo, Austria-Hungary declares war on Serbia, effectively beginning the First World War -
German Empire
Germany entered into World War I on August 1, 1914, when it declared war on Russia. ... Italy, which was allied with Germany and Austria-Hungary before World War I, was neutral in 1914 before switching to the Allied side in May 1915. Historians have vigorously debated Germany's role. -
Ottoman Empire
The Ottoman Empire joined the Central Powers to form the Triple Alliance with the signing of the August 1914 Turco-German Alliance. Turkey formally entered World War I on 28 October 1914 with the bombing of Russian Black Sea ports. The Triple Entente, or Allied Powers, declared war on the Ottoman Empire on November 4. -
Bulgaria
The Kingdom of Bulgaria participated in World War I on the side of the Central Powers from 14 October 1915, when the country declared war on Serbia, until 30 September 1918, when the Armistice of Thessalonica came into effect.