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.

In the late 1940s and 1950s, U.S. officials sought to stabilize Iraq. They helped to negotiate a withdrawal of Iraqi military forces from the Palestinian theater as part of a broader plan to end the first Arab-Israeli war. They encouraged the IPC to increase oil production and to share a larger portion of revenues with the Iraqi government. They provided economic and military aid to the Iraqi government.

By 1955, the United States enlisted Iraq as a charter member of the Baghdad Pact, an anti-Soviet defense partnership linking Iraq, Iran, Pakistan, Turkey, and Britain, with informal U.S. backing.

Briefly, it appeared that the United States had found a formula for ensuring the long-term stability and anti-communism of Iraq.

But that appearance evaporated quickly in July 1958, when a coalition of Iraqi military officers, disillusioned by the monarchy's subservience to the West and inspired by revolutionary leader Gamal Abdel Nasser of Egypt, overthrew the king in a bloody coup d'état and instituted a new regime with a distinctly anti-western flavor.

In reaction, President Eisenhower sent U.S. Marines into Lebanon to avert a copycat rebellion there, but he rejected the notion of military intervention to reverse the revolution in Baghdad as too difficult tactically and too risky politically.

The Iraqi revolution of 1958 clearly marked the failure of the U.S. quest to align the pro-Western, British-built, royalist government of Iraq on the Western axis in the Cold War.

II. Managing Chronic Instability, 1958-1979

The second phase of U.S.-Iraqi relations was defined by the political instability in Baghdad that came in the wake of the fall of the Iraqi monarchy in 1958.

The revolution of 1958 was followed by others in 1963, 1968, and 1979. Other revolts reportedly were attempted along the way and political and ethnic-cultural conflicts generated persistent strife throughout the era.

Nationalists aiming to remove the vestiges of foreign imperialism clashed with indigenous communists who sought political influence. The Kurdish population of northern Iraq resisted the authority of Arabs in Baghdad.

Although internally unstable, Iraq emerged as an independent power on the international stage. Its government pursued neutralism in the Cold War and flirted with the Soviet Union and other communist states. It also sought political influence among Arab states and contested Egyptian dominance of the Arab community of nations. Iraq remained technically at war and occasionally skirmished with Israel. Management of the delicate Kurdish problem in the 1970s led Baghdad into alternating conflict and cooperation with Iran.

In the 1958-1979 era, the United States pursued interlocking goals in Iraq. On behalf of U.S. political and economic interests in the country and the region, U.S. officials sought a stable political relationship with the government in Baghdad, aimed to prevent the rise of communism within the country and to deny the Soviet Union influence there, and strove to prevent Iraq from becoming a source of regional conflict or war.

U.S. leaders showed little support for democracy in Iraq or the advancement of its people, eschewing any such liberal political goals on behalf of the primary objective of keeping Iraq free of communism.

For several years after the 1958 coup, U.S. officials accrued some successes in achieving its goals. They maintained diplomatic relations, negotiated the peaceful termination of the Baghdad Pact, averted conflict in an Anglo-Iraqi showdown over Kuwait in 1961, dispensed foreign aid to Iraq, and promoted business opportunities there. In light of evidence that the Soviet Union backed Iraqi Kurds, officials in Washington did nothing to alleviate the Iraqi suppression of that ethnic group.

Nonetheless, U.S.-Iraqi relations declined in the late 1960s.

Iraq severed diplomatic relations in 1967 because it considered the United States complicit in Israeli military conquests during the so-called Six Day War of June 1967. In the early 1970s, Iraq nationalized U.S. petroleum interests and partnered with the Soviet Union to develop its oil capacity.

U.S. officials covertly equipped Kurdish rebels in order to weaken the Iraqi government. Although Iraq neutralized the Kurdish problem through diplomacy with Iran, it criticized foreign powers that backed the Kurds and it displayed renewed anti-U.S. tendencies in its approach to Arab-Israeli issues in the late 1970s.

III. The Initial Challenge of Saddam Hussein, 1979-1989

The third phase in U.S.-Iraqi relations opened in 1979, when Saddam Hussein seized power in Baghdad. Quickly, Hussein brutally suppressed all domestic rivals and thereby built internal stability in Baghdad, ending decades of political turmoil.

A secularist, Hussein also positioned himself as a vital bulwark against Islamic fundamentalism in Iran, where the Ayatollah Ruhollah Khomeini took power in 1979 and declared an intention to export his revolutionary ideals across the region. [Read Origins on U.S.-Iranian Relations]

Mounting tension between the two gulf powers erupted into war in September 1980, when Hussein ordered the Iraqi army to launch a full-scale invasion of Iran. Iraq initially occupied 10,000 square miles of Iranian territory before Iran stymied the Iraqi thrust. Iran then gradually recaptured its territory, leading to a stalemate in the battle front by 1982.

A series of massive land offensives proved to be ineffective at breaking the deadlock. Yet the war ground on, widened by missile attacks on cities and by mutual assaults on oil tankers on the Gulf. By 1988, the two states together counted more than one million casualties.

President Ronald Reagan gradually led the United States into involvement in the Iran-Iraq War. Initially, Reagan continued the policy he inherited from Jimmy Carter of practicing strict neutrality in the conflict. By 1982, however, the government in Washington began to shift toward a position of supporting Iraq.

Iran's military advances worried U.S. officials that it might gain political influence across the region and its support of anti-American kidnappers in Lebanon soiled its reputation in the West. Despite Hussein's political despotism, U.S. leaders reinterpreted Iraq as a more benign power and as a vital bulwark against Iranian expansionism.

Thus the Reagan Administration provided Iraq with economic aid, restored diplomatic relations, shared intelligence information about Iranian military forces, and otherwise engaged in what it called a "tilt" toward Iraq designed to ensure its survival. U.S. officials also suspended their protests of Iraq's use of weapons of mass destruction against Iranian troops and domestic rivals.

By 1987, the Reagan Administration even assumed limited military involvement in the war on behalf of Iraq. When Iran attacked oil tankers carrying Iraqi oil to world markets, Reagan ordered the U.S. Navy to patrol the Gulf and protect those tankers. Armed clashes occurred between U.S. and Iranian naval vessels, peaking in late 1987 and mid-1988.

Taking advantage of the relaxation of Cold War tensions, Reagan also worked with Soviet and other world leaders to fashion a United Nations ceasefire resolution that provided a legal framework for ending the hostilities. Iraq promptly accepted the ceasefire but Iran refused, demanding that Iraq first must agree to pay war reparations. Pressured by the U.S. Navy, however, Khomeini eventually accepted the ceasefire in July 1988.

From the U.S. perspective, the Iran-Iraq ceasefire promised to restore a semblance of stability to the Gulf region for the first time in a decade. Peace on the battlefields would end the bloodletting between the two belligerents and restore lucrative commerce. At the same time, the dramatic improvement in U.S.-Soviet relations diminished the traditional U.S. concern that communism would sweep across the region.

With Khomeini contained, U.S. officials hoped that Saddam Hussein would lead his country and the Middle East into an era of peace, prosperity, and moderation. Yet, U.S. officials refrained from addressing Hussein's dreadful record of human rights abuses, his aggressive tendencies, and his political despotism; nor did they take steps to curb the Western thirst for Middle East oil.

Subsequent events would demonstrate that such U.S. officials unwisely built a Middle East strategy on the unstable foundation of the Hussein regime.

IV. The Gulf War and Containment, 1989-2003

The fourth era in U.S. policy toward Iraq featured a short, indecisive war between the two states followed by a "long decade" of consequential complications.

The military clash originated in Saddam Hussein's decision, in the aftermath of the Iran-Iraq War, to seek territorial and economic gains at the expense of Kuwait. In 1989 and 1990, Hussein signaled a growing intention to use force to against the tiny emirate.

Hussein's aggressiveness was prompted by multiple incentives: a desire to capture lucrative oil assets and thus relieve the financial burdens incurred in the war against Iran; a quest to achieve stature among neighboring leaders and to rally domestic public opinion behind his regime; and a hope of capturing land that, many Iraqis believed, had been misappropriated to Kuwait decades before.

The George H.W. Bush administration reacted to the mounting tensions by using the relatively stable relationship that emerged during the 1980s as a brake on Iraqi recklessness. Viewing Iraq as an important counterweight against Iranian expansionism, Bush offered political friendship and economic incentives to lure Hussein into proper behavior.

When tensions rose and Hussein moved 100,000 troops to the Kuwait border, Bush also bolstered the U.S. naval presence in the Gulf and warned Hussein against instigating military action.

Yet Bush continued to deal with Hussein constructively—while ignoring his abysmal human rights and foreign policy records—on the calculation that firmer measures might actually provoke the very aggressive behavior that the United States hoped to prevent.

Iraq's full-scale military invasion of Kuwait on August 2, 1990 clearly demonstrated Hussein's reckless aggressiveness and the futility of Bush administration efforts to deal with him on friendly terms.