Iraq War, origins of invasion
A number of factors, stretching back over twenty years, formed the origins of the invasion in the Iraq War. While it was a centerpiece of the foreign policy of George W. Bush, other Presidents had taken action against Iraq, and there were strong national and international faction urging regime change.
While the United States tilted toward Iraq in this war, for a variety of reasons, it supported, for some time, Kurdish insurgency against Saddam.
After the Gulf War in 1991, United Nations Resolution 687 specified that Iraq must destroy all weapons of mass destruction (WMD). A large amount of WMDs were indeed destroyed under UN supervision (UNSCOM). Two no-fly zones were also instituted in northern and southern Iraq where Iraqi military aircraft were prohibited from flying. The United States and the United Kingdom (and France until 1998) patrolled these zones in, respectively, Operation NORTHERN WATCH and Operation SOUTHERN WATCH.
According to Richard Clarke, the U.S. found a press report, in April 1993, of an attempt, by the Iraqi intelligence service, to assassinate former President George H. W. Bush while he was visiting Kuwait. After confirmation by the CIA and FBI, a retaliatory missile strike was delivered in June of that year. Searches of the records of the Iraqi service after 2003 did not provide hard evidence of such a plot, but reporter Michael Isikoff, often skeptical about U.S claims about Iraq, agreed the records might have been destroyed. 
The 1996 Khobar Towers bombing attacked forces, in Saudi Arabia, conducting SOUTHERN WATCH. This attack, however, appears to have been sponsored by Iran.
However, by late 1997, the the Clinton administration became dissatisfied with Iraq’s increased unwillingness to cooperate with UNSCOM inspectors. As a result of widespread expectations that the Clinton administration would decide to act with military force, the UN weapons inspectors were evacuated from the country. Iraq and the United Nations agreed to resume weapons inspections, but Saddam Hussein continued to obstruct UNSCOM teams throughout the remainder of 1998.
Congress passed the Iraq Liberation Act in October 1998:
It should be the policy of the United States to support efforts to remove the regime headed by Saddam Hussein from power in Iraq and to promote the emergence of a democratic government to replace that regime. 
During the campaign, Bush had criticized President Clinton as too widely engaged in too many conflicts, acting as the “world’s policeman.” In the end, President Bush believed Clinton had lacked the necessary resolve to hold Saddam Hussein accountable for his failure to comply with UN resolutions. Bush also questioned America’s membership in NATO and involvement in UN diplomacy, which led some to believe he was moving towards a more isolationist view of foreign policy.
At the same time, Bush continued to favor executing the policy President Clinton had approved but not acted on: to actively proceed to effect regime change in Iraq.
In December 1998, President Clinton authorized military action against Iraq. Between December 16 and 19, 1998, US and UK missiles and aircraft attcked military and government targets in Iraq in Operation DESERT FOX. It was widely understood that the Clinton administration intended Operation Desert Fox to be not merely a campaign of punishment for Iraq’s failure to cooperate but also to weaken the regime in advance of orchestrated efforts to cause regime change. In that respect, Clinton administration policy was ineffective.
As a result of Iraq’s barring inspectors from the country, UNSCOM inspections of Iraq’s WMD effectively came to an end and in March 1999, the UN concluded that the UNSCOM mandate should end. In December 1999, the UN passed UN Security Council Resolution 1284, setting up UNMOVIC (United Nations Monitoring, Verification and Inspection Commission), headed by Swedish diplomat Hans Blix, which was to identify the remaining WMD arsenals in Iraq. Because UNMOVIC was banned from Iraq, the world had to rely on indirect evidence, most of which turned out to be false or inaccurate. Iraq policy during the remainder of the Clinton presidency was marked by a return to the containment regime that existed before Operation Desert Fox, but now without the benefit of direct intelligence.
Bush Administration Policy
Iraq had been a high priority for George W. Bush during the campaign, and even more so after the election. Before the inauguration, Dick Cheney sent a message to the outgoing Secretary of Defense, William Cohen, "We really need to get the president-elect briefed up on some things [including a serious]] discussion of Iraq." Bob Woodward put it that Bush said "I was not happy with our policy", but it was not yet a first priority.
When Bush and Clinton met in the days of transition, on December 19, 2000, Clinton said that his understanding of Bush's priorities, from reading his campaign statements, were national missile defense and Iraq. Bush said that was correct. Clinton suggested Bush consider other priorities, including al-Qaeda, Middle East diplomacy, North Korea, the nuclear competition between India and Pakistan, and, only then, Iraq. Bush did not respond.  Cheney reinforced the already existing, but not well-known, policy of regime change in Iraq, specified by the 1998 Iraq Liberation Act.
On January 10, the new national security team was briefed on the no-fly programs, Operation SOUTHERN WATCH and Operation NORTHERN WATCH, and the graduated responses in effect if the Iraqis fired on U.S. aircraft. Several days later, they were briefed on CIA operations, including Iraq, but the tree major priorities were:
- Osama bin Laden
- Worldwide proliferation of weapons of mass destruction
- Rise of the Chinese military
Iraq was not discussed in detail.  There was, however, a meeting of "principals", chaired by Assistant to the President for National Security Affairs Condaleeza Rice on February 5, which did include Cheney, Colin Powell, and Deputy Director of Central Intelligence John McLaughlin as a substitute for DCI George Tenet. This meeting was focused on Iraq policy. The decision was to reduce the number of no-fly sorties but to increase the intensity of response.
Policy before 9/11 Attacks
Because Iraq was known to have had and used WMD in the past and because Iraq had blocked UN supervision of the destruction of its WMD, there remained great uncertainty about Iraq’s WMD arsenal. The Bush administration made Iraq of central importance to its national security policy, called the Bush Doctrine. Francis Fukuyama, who was not totally for or against the war, discusses the Doctrine in America at the Crossroads: Democracy, Power, and the Neoconservative Legacy. The doctrine is most fully expressed in the administration’s National Security Strategy of the United States of America, published in September 2002. In it, the President states:
We will disrupt and destroy terrorist organizations by (…) direct and continuous action using all the elements of national and international power. Our immediate focus will be those terrorist organizations of global reach and any terrorist or state sponsor of terrorism which attempts to gain or use weapons of mass destruction (WMD) or their precursors.
The Bush national security doctrine invoked a doctrine that it called "preemption" of potential threats, but the attitude toward Iraq was more one of preventive war, or military action to stop development of capabilities in weapons of mass destruction or terrorism. The usual meaning of preemptive attack is to stop an imminent and identifiable enemy action.
On February 16, 2001 a number of US and UK warplanes attacked Baghdad, nearly two years before the start of the Iraq war. . An officer in the Joint Staff notified Rice, who notified the President. Rumsfeld was not told, and was furious, because the chain of command went through him. Rumsfeld told Woodward that as the first Secretary of Defense to serve again, many years later, he was determined to play it better and have near-total control. Rumsfeld, a college wrestler, said "If someone does not know how to wrestle, he will get hurt. If you don't know how to move, you will get a black eye. Same in Defense." Rumsfeld wanted the Administration to be "forward-leaning" rather than reactive. 
Policy discussions continued at the Deputies level, where Deputy Secretary of State Richard Armitage, Powell's best friend, faced Deputy Secretary of Defense Paul Wolfowitz. One of the Iraq issues was Ahmed Chalabi, who was distrusted by State and CIA, but attractive to Defense. In January 2002, Time Magazine reported that since President Bush took office he had been grumbling about finishing the job his father started. 
Iraqi WMD and the War on Terror
At the top level, it does not appear that any top government leaders wanted to strike Iraq immediately after 9/11. It had been discussed; some of Rumsfeld's notes suggest raising the question with Wolfowitz. In a meeting on the 15th, none of the principals wanted to attack Iraq at first; Woodward reported Cheney said "If we go after Saddam Hussein, we lose our rightful place as good guy." Wolfowitz suspected Saddam but had no proof. Bush told Woodward, two years later, said it changed his attitude toward "Saddam Hussein's capability to create harm...all his terrible features became much more threatening. Keeping Saddam in a box looked less and less feasible to me." 
The administration included Iraq in a series of states it considered acutely dangerous to world peace. In his 2002 State of the Union President Bush called Iraq part of an “axis of evil” together with Iran and North Korea. In this address the president also claimed the right to wage a preventive war, as distinct from a preemptive attack. Early in 2002, the administration began pressuring Iraq as well as the international community on greater compliance by Iraq with UN resolutions.
Not all the senior officials of the administration treated attacking Iraq as a high priority. Some believed there was no case, while others felt that Afghanistan needed a higher priority. While Colin Powell eventually argued for Iraqi WMD before the United Nations, he and his deputy, Richard Armitage, internally raised questions. Senators Joe Biden, Richard Lugar, and Chuck Hagel were drafting legislation to limit Bush's authority; Biden said he was getting support from Powell and Armitage. 
There was a concern that Saddam, as opposed to equally brutal dictators such as Hafiz Assad of Syria, was not a rational actor, and might take irrational risks.  Nevertheless, he also had a strong need for control, and the questions arise why he would risk a major retaliation from a direct attack on the US, or why he would give away control of WMD to a terrorist group.
Douglas Feith said never heard Bush say "we should [go to war] simply or primarily to help a foreign pro-democracy movement oust a dictator. Neocons, including myself, were commonly accused of wanting to spread democracy by the sword...In my view, the reason to go to war with Iraq was self-defense." 
In the spring of 2002, Richard Haass, head of the Policy Planning Staff at the U.S. Department of State, met with Condoleeza Rice, and expressed State's concerns about war with Iraq. She surprised him by saying "Save your breath. The President has made up his mind." Haass described it as "A decision was not made — a decision happened, and you can't say when or how. 
On January 13, 2003, Bush met with Powell to tell him he had decided to go to war, "The inspections are not getting us there...I really think I'm going to have to do this." He asked Powell if he would or would not support the decision, and Powell agreed; Powell still would attempt to avoid war through diplomatic channels. Bush told Chief of Staff Andy Card of the meeting, and Card believed that Powell had false hope of avoiding war. 
Bush's vision was not simply ousting Saddam, but creating a democracy. This had been the goal of the Project for the New American Century in its 2000 policy paper, "Rebuilding America's Defenses".; the concept involves using preventive war, if necessary, to install democracies; it assumes societies will accept democracies. According to Bob Woodward, Bush had said,
We've got an obligation to go stand up a democracy. We can't go get some former [Iraqi] general and say, Okay, now you're the dictator in Iraq. We've got to fundamentally change the place. And we've got to give the Iraqi people a chance at those fundamental values we believe in.
Cheney thought that too many people in the State Department, including Powell, did not support Bush's vision. Cheney, therefore, tried to keep control of the implementation, generally in concert with Rumsfeld, his protege and bureaucratic opponent of Powell. While Rice probably was personally closer to Bush than the others, she was not as strong an infighter.
- Richard A. Clarke (2004), Against all Enemies: Inside America's War on Terror, Free Press, Simon & Schuster, ISBN 0743260244, pp. 80-84
- Alfred B. Prados (November 20, 2002), Iraqi Challenges and U.S. Responses: March 1991 through October 2002, Congressional Research Service
- Michael Isikoff (March 31, 2008), "Saddam’s Files: They show terror plots, but raise new questions about some U.S. claims.", Newsweek
- Iraq Liberation Act of 1998
- Cameron G. Thies. “From Containment to the Bush Doctrine: The Road to War with Iraq.” In: John Davis ed. Presidential Policies and the Road to the Second Iraq War. Aldershot (UK)/Burlington (VT):Ashgate, 193-207, here p. 200.
- Ali A. Allawi. The Occupation of Iraq: Winning the War, Losing the Peace. New Haven (Conn.): Yale University Press, 2007, p. 72.
- Bob Woodward (2004), Plan of Attack, Simon & Schuster, ISBN 074325547X, pp. 7-8
- Michael R. Gordon, Bernard E. Trainor (2006), COBRA II: the inside story of the invasion and occupation of Iraq, Pantheon, ISBN 0375422625, p. 14
- Woodward, p. 12
- National Security Strategy of the United States of America (2002), The White House, September 2002. (Page 6 in the printed edition). Retrieved May 8, 2008.
- "U.S., British warplanes hit targets outside Baghdad", CNN, 16 February 2001
- Woodward, pp 14-19
- Daniel Eisenberg (5 May 2002), ""We're Taking Him Out"", Time Magazine
- Woodward, pp. 25-27
- 2002 State of the Union address, President George W. Bush, January 29, 2002. Retrieved May 8, 2008.
- Michael Isikoff, David Corn (2006), HUBRIS: the Inside Story of Spin, Scandal and the Selling of the Iraq War, Crown/Random house, ISBN 0307346811, p. 127
- Kenneth M. Pollack (2002), The Threatening Storm: the Case for Invading Iraq, Random House
- Francis Fukuyama (2006), America at the Crossroads: Democracy, Power, and the Neoconservative Legacy, Yale University Press, ISBN 0300113994,pp. 88-90
- Douglas J. Feith (2008), War and Decision: Inside the Pentagon at the Dawn of the War on Terrorism, Harper, ISBN 9780060899738 , p. 234
- George Packer (2005), The Assassins' Gate, Farrar, Straus and Giroux, ISBN 0374299633, p. 45
- Woodward, pp. 269-273
- Project for the New American Century (September 2000), Rebuilding America's Defenses: Strategy, Forces and Resources for a New Century
- Woodward, Plan of Attack, p. 284