Under a cloak of early morning darkness on December 18, 2011, some 500 U.S. soldiers at Camp Adder in southern Iraq boarded 110 military vehicles and drove off quietly into the night, without having notified their local Iraqi colleagues of their departure. On heightened alert, the convoy maneuvered steadily to the south and reached the border of Kuwait some five hours later.

This departure of the 3rd Brigade Combat Team of the 1st Cavalry Division of the U.S. Army—conducted in secrecy in hope of avoiding any opportunistic attacks by local adversaries—marked the end of a nearly nine-year-long U.S. military adventure in Iraq.

Although the final convoy departed Iraq without incident, it left behind a legacy of a war that was controversial in origin, costly to Iraqi civilians and American soldiers, and inconclusive in outcome.

The 2003 U.S. military invasion of Iraq and the extended occupation that followed were certainly the most dramatic and significant events in the long history of U.S. relations with Iraq. During the nine decades since Iraq was established as a separate state in the aftermath of World War I, the policy of the United States towards it can be divided into five phases.

In each period, the United States pursued distinct goals in Iraq—goals that reflected the growing interest of the United States in the Middle East, the increasing political and military influence of Iraq, and the evolution of U.S. interests in a rapidly changing international context.

I. Genesis of U.S.-Iraqi Relations, to 1958

Prior to World War II, the U.S. government took very little interest in Mesopotamia (Greek for "land between the rivers," in reference to the basin between the Tigris and the Euphrates, and a name used before World War I for the territory that generally formed modern Iraq).

The first Americans to encounter the region were evangelical Christian missionaries who swarmed across it beginning in the 1830s and who built hundreds of churches, schools, and medical facilities by the turn of the twentieth century. In 1880-1920, archaeologists from American universities conducted field work in Mesopotamia in the hope of discovering physical artifacts that would corroborate Biblical history.

U.S. oil corporations began probing Mesopotamia for commercial opportunities in the 1910s, gaining a 23.75 percent share in the Iraq Petroleum Company (IPC) in 1928. Within a decade, the IPC discovered a massive oil field near Kirkuk and built a network of wells, pipelines, and production facilities that earned it considerable wealth.

U.S. government involvement in early Iraq was limited. President Woodrow Wilson envisioned a liberal post-World War I political system that would include self-determination for Iraqis and other peoples of the former Ottoman Empire, but he was unable to promote that vision effectively.

In the 1920s and 1930s, U.S. diplomats generally deferred to British officials, who managed Iraq as a League of Nations mandate, demarcated its national borders, and built it into a pro-Western monarchy.

When a threat developed that Nazi Germany might gain political dominance in Baghdad during World War II, U.S. diplomats endorsed the British military suppression of Rashid Ali al-Gailani, a pro-Nazi Iraqi who briefly occupied the position of prime minister. With American backing, the British restored the monarchy, which cooperated with Allied war aims and strategy.

Post-World War II international dynamics gradually drew the United States into a deeper political relationship with Iraq. The onset of the Cold War raised fears in Washington about Soviet expansionism into the Middle East and generated a determination among American leaders to prevent the spread of communism in Iraq.

Financially drained by the world war, Britain proved unable to maintain its position of imperial dominance in the country. Intra-regional tensions, most notably the conflict over Palestine that erupted as the first Arab-Israeli War of 1948-49, also destabilized the region. The emergence of anti-Western nationalism—a reaction to the legacy of British imperialism and U.S. support for Israel, among other factors—undermined the local popularity of the pro-Western monarchy in Baghdad.