It started after British amphibious landings in 1914 which sought to protect Anglo-Persian oil fields in Khuzestan and the Shatt al-Arab.

Fighting began after an amphibious landing by an Anglo-Indian division at the fortress of Al-Faw before rapidly advancing to the city of Basra to secure British oil fields in nearby Persia (now Iran).

Following the landings, Allied forces won a string of victories along the Tigris and Euphrates Rivers, including repulsing an Ottoman attempt to retake Basra at the Battle of Shaiba.

The campaign ended with a British mandate over Mesopotamia being established and change of the power balance following the Ottoman expulsion from the region.

In Turkey, elements of the last Ottoman parliament still claimed parts of modern-day Iraq such as Mosul as being Turkish, leading to Allied occupation of Constantinople.

[11][12] The oil pipeline to transport the Persian petroleum ran alongside the Karun River into the Shatt al-Arab waterway, with refineries based on Abadan Island in the area.

[13][14] The petroleum in this region was vital for Britain's new line of oil-fired turbine based dreadnoughts as well as toluol for the production of explosives.

In addition to oil, Britain wanted to retain its dominance of the Persian Gulf, show support for local Arabs, and demonstrate power to the Ottomans, with Sir Edmund Barrow, military secretary to the Indian Office, stating, "ostensibly to protect the oil installation but in reality to notify the Turks that we mean business and to the Arabs that we are ready to support them".

[14] In addition to these factors, growing German influence in the region caused by the creation of the Berlin-Baghdad railway was of concern to London.

However, the Gulf was not a priority to London as the Suez Canal and Western Front were seen as more important, whereas Delhi planned an offensive campaign to take Baghdad.

[17] On 6 November 1914, British offensive action began with the naval bombardment of the old fort at Fao, located at the point where the Shatt-al-Arab meets the Persian Gulf.

At the Fao Landing, the British Indian Expeditionary Force D (IEF D), comprising the 6th (Poona) Division led by Lieutenant General Arthur Barrett with Sir Percy Cox as Political Officer, was opposed by 350 Ottoman troops and 4 guns.

The same month, the ruler of Kuwait, Sheikh Mubarak Al-Sabah, contributed to the Allied war effort by sending forces to attack Ottoman troops at Umm Qasr, Safwan, Bubiyan, and Basra.

[25] Mubarak's participation and previous exploits in obstructing the completion of the Baghdad railway helped the British safeguard the Persian Gulf by preventing Ottoman and German reinforcement.

After establishing order in the town the English forces continued their advance, and at the Battle of Qurna they succeeded in capturing Subhi Bey and 1,000 of his troops.

Although the irregulars proved ineffective, the Ottoman infantry launched a series of relentless attacks on the fortified British camp and later attempted by bypass it.

In late September 1915, amidst the recent defeat of Serbia and entry of Bulgaria into the war and concerns about German attempts to incite jihad in Persia and Afghanistan, Grey (Foreign Secretary) and other politicians encouraged a further 100-mile push to Baghdad.

The CIGS Murray thought this logistically unwise, but Kitchener advised the Dardanelles Committee (21 October) that Baghdad be seized for the sake of prestige, then abandoned.

Further attempts to advance in Mesopotamia were ordered by the politicians on the War Committee (18 September), including Curzon and Chamberlain, who argued that there would be no net savings in troops if a passive policy in the Middle East encouraged Muslim unrest in India, Persia and Afghanistan, and despite the opposition of Robertson.

[36] After the defeat at Kut, the British made a major effort to improve the ability to move men and equipment into theatre, and keep them supplied.

The new commander, General Maude, with secret orders from Robertson not to attempt to take Baghdad,[35] was given additional reinforcements and equipment.

[39] Robertson changed his mind when it seemed that the Russians might advance to Mosul, removing any Turkish threat to Mesopotamia, and authorised Maude to attack in December 1916.

The British resumed their offensive in late February 1918 capturing Hīt and Khan al Baghdadi in March, and Kifri in April.

General Marshall, following instructions from the War Office that "every effort was to be made to score as heavily as possible on the Tigris before the whistle blew",[45] went on the offensive for the last time.

Within two days it covered 120 kilometres, reaching the Little Zab River, where it met and engaged Ismail Hakki Bey's Sixth Army, most of which was captured in the resulting Battle of Sharqat.

General Marshall accepted the surrender of Khalil Pasha and the Ottoman 6th Army on the same day, but Cobbe did not hold his current position as the armistice required, and continued to advance on Mosul in the face of Turkish protests.

Misak-ı Milli stated that the Mosul Province was a part of their heartland, based on a common past, history, concept of morals and laws.

Presumably, from a British perspective, if Mustafa Kemal Atatürk succeeded in securing the stability in his efforts to establish Republic of Turkey, he would have turned his attention to recovering Mosul and penetrate into Mesopotamia, where the native population would probably join him.

The worst part of the transfer was the 250 miles (400 km) forced march from Mosul to Ras-el-Ain for which they were allowed just a quart (1.1 l) of water, and many were clubbed to death by guards.

[51] Applying that same ratio to the Mesopotamia Campaign produces a total battle casualty count of about 89,500 (13,069 KIA, 56,000 WIA, 20,404 POW).