The stomach-wrenching violence in Iraq — not to mention the horrendous civil war in Syria, the chronic unrest in Palestine/Israel, and problems elsewhere in the Middle East — are direct consequences of the imperialist acts of the British and French governments at the end of World War I, the history-altering catastrophe that began 100 years ago this August 4.
The story has been told many times. The government of Great Britain wanted to disrupt the Ottoman Empire's ability to help Germany and the Austro-Hungarian empire in the Great War. So the British dispatched personnel, most famously T.E. Lawrence (Lawrence of Arabia), to persuade the Arab leaders to revolt against the Turks, in return for which they would gain their independence in (roughly) the Levant (what today is Israel/Palestine, Jordan, Syria), Mesopotamia (Iraq), and the Arabian Peninsula. The Arab leadership agreed and proceeded to obstruct the Turks' war efforts.
In the 1915–16 correspondence between the British High Commissioner in Cairo, Sir Henry McMahon, and Arab leader Hussein bin Ali, McMahon acknowledged Hussein's demand for independence in most of the Levant (Palestine included) and the Arabian peninsula:
Subject to the above modifications, Great Britain is prepared to recognize and support the independence of the Arabs in all the regions within the limits demanded by the Sherif of Mecca [Hussein].