You answered - Russia
The Ottoman Empire was brought into the war when Russia mobilized against Germany. Minister of War for the Empire, Enver Pasha, had signed a defensive military alliance with Germany which made Prime Minister Sait Halim livid as he thought it was best for the Empire to remain neutral. On 2 November, Russia declared war on the Ottoman Empire. France and the British Empire, Russia's wartime allies, followed suit on the 5th and it was the Empire's eventual defeat that led it to split.