At the start of the 20th century Turkey remained at the head of the Ottoman Empire which extended into parts of modern-day Greece, Bulgaria, the Middle East and controlled access to the Mediterranean Sea via the Aegean Sea. Turkey had been engaged in the Balkan Wars of 1912 and 1913 which gave its army fighting experience if nothing else.
Turkey formally entered the war in October 1914, when two Turkish ships attacked Russian ports, Russia replied by declaring war on Turkey, closely followed on the 5th November by her allies as Britain and France also declared war on Turkey.
The First Sea Lord, Winston Churchill, devised a plan which he believed would knock Turkey out of the war and relieve the pressure on the Russian border. An amphibious operation was planned which involved French and British forces, as well as Australian and New Zealand troops who formed the ANZACs. The first landings took place in April and initially they were successful with advances being made, however, Turkish troops were quickly re-organised and deployed into positions which checked the Allied landings and prevented any further territorial gains. It was a stalemate and the campaign ground to a stop, with casualties mounting for no advantage.
Finally, it was decided to halt the campaign and in December 1915 the ANZACs were withdrawn, closely followed by the British and French on the 9th January 1916.