By 1914, the Turkish Empire was known as the "sick man of Europe". His Balkan possessions had been dramatically reduced in 1912, when the First Balkan War had seen Greece, Albania, Bulgaria and Serbia free themselves from Turkish rule.
On the outbreak of war, Germany courted Turkey in secret, and they entered the war on 5th November 1914, declaring war on France, Britain and Russia.
One of the most disastrous campaigns of the war, the Dardanelles campaign was fought on Turkish soil, as the ANZAC (Australian and New Zealand Army Corps) tried to force a passage through the straits to the Black Sea, at once supplying Russia from the Mediterranean and taking Istanbul, the capital of the Ottoman Empire.
The attack, largely the brainchild of one Winston Churchill, failed and, after much misery and hardship for the ANZACs, they were withdrawn, having failed in most cases to even get off the beaches.
As well as the disastrous Dardanelles campaign, British troops also fought in the deserts of Turkish-owned Mesopotamia. Invading from Suez in Egypt, and landing near Kuwait, British troops had taken Jerusalem and Baghdad by September 1917.
In the north, Russia also invaded Turkish territory, but after the dramatic collapse of the Russian army during the Revolution in October 1917, the Turkish army swept north and entered Russian territory. By the Russian surrender of Spring 1918, the Turkish forces had taken Baku on the Caspian Sea.