The Indian Army, also called the British Indian Army, was involved in World War I as part of the British Empire. More than one million Indian troops served overseas, of whom more than 60,000 died during the war.

The Mesopotamian campaign or Mesopotamian front was a campaign in the Middle Eastern theatre of World War I fought between the Allies represented by the British Empire, troops from Britain, Australia and the vast majority from British Raj, against the Central Powers, mostly the Ottoman Empire. It started after British amphibious landings in 1914 which sought to protect Anglo-Persian oil fields in Khuzestan and the Shatt al-Arab. However, the front later evolved into a larger campaign that sought to capture the key city of Baghdad and divert Ottoman forces from other fronts. It ended with the Armistice of Mudros in 1918, leading to the cession of Iraq and further partition of the Ottoman Empire.