The situation in the Middle East was complex, the Ottoman Empire was on the wane but still occupied most of the area; a Muslim nation but not Arabic. The German influence created by the Berlin to Baghdad railway was to prove a deciding factor on the outbreak of hostilities, Turkey aligned themselves with Germany.
The extended Turkish Army did however have many Arab units and some high ranking Arabs too. Some saw this train of events to be an opportunity for the long hoped for Arab Nation to emerge and be independent.
The region though was split and oil interests muddied the waters. The British had its main influence in Cairo, Aden ( a major staging post) and the southern parts of what was then Mesopotamia and Persia and fell mostly under military orders from India. The French had designs on Syria and of course much against the British Government's wishes, France, had gone ahead and built the Suez Canal. The Canal was to prove a bonus, providing a barrier and preventing the Turkish Army from crossing into Egypt.
The British Indian Army had already started an offensive to protect its interests in southern Mesopotamia. In December 1915 the British had reached just south of Baghdad. Here they met determined Turkish forces and with the British supply lines already stretched they were forced to retreat after the Battle of Ctesiphon. They fell back to Kut. It was not an ideal place but they dug in under extreme pressure. Here the Turkish forces held the British. The Siege of Kut, as it was known, was a huge failure for the British; during the siege attempts were made to resolve the situation.
Relief expeditions were sent to attack the Turks and air drops to help those under siege but failed. In a last ditch attempt to resolve the situation the British Government sent from the Arab Bureau in Cairo, Aubrey Herbert and Lawrence, who respectively spoke fluent Turkish and Arabic. Their charge was to try to bribe the Turks into releasing the British Allied Army (Herbert) and to try to incite the Arabs to revolt within the Turkish Army (Lawrence). They had at their disposal £1m, although it is believed it was upped to £2m. It failed and after negotiations the wounded were allowed to leave and safe passage allowed for Aubrey and Lawrence.
In all the campaign cost the British Allied forces some 30,000 men either killed or wounded. The condition of the wounded men being evacuated was appalling and would be the subject of questions asked in Parliament later. This defeat came only 3-4 months after the retreat from from Gallipoli. Kut to my mind must have had an influence on Lawrence and his attitude to the Turks later on in the campaign.