If not for the oil WTF did we go for?
For me to say 'here is the answer', it would imply I have some 'evidence' like aq document from the people who decided confessing their reasons.
Without that, it can only be informed speculation, but clearly there were reasons for us to speculate about.
Here's my basic opinion, saying up front I only have partical info so it's incomplete.
1. Our Republican presidents have had 'interests' or 'forces' behind them that they enable for some time now. National security related interests.
We could go back as far as Eisenhower - this cropped up post-WWII - but it wasn't the same then. The CIA was in its baby stages, but was already picking and choosing governments and assassinations around the world. It was already undermining the incoming President-elect Kennedy by ordering the assassination of the leader Kennedy was planning to work with in Africa for policies the CIA did not care for, and in his first few months trying to mislead the President into an invasion he didn't want of Cuba (for which he fired the #1 and #2 men at the CIA, beginning a period of very strained relations between him and some of these interests).
But you can see it more with Nixon/Ford - funny enough, powerful forces there included the Cheney Rumsfeld team, who rose in power to where they were Ford's Chief of Staff and Secretary of Defense. Nixon had begun a process of detente, saying it would end the cold war - Cheney and Rumsfeld were not for that. They began creating stories of secret new Soviet weapons to terrify the country - with no evidence for them proving the secret weapons existed. The CIA strongly disagree with them - no matter. They talked ford into creating a commission, called "Team B", which included... wait for it... Paul Wolfowitz, which concluded that my gosh yes, the Soviets had terrifying new weapons. They created the "Committee on the Present Dange" - yes, that was the actual name - which had the purpose of spreading the message to the country to fear the Soviet Union and these new weapons, and advocate large increases to the military budget. It worked - the nation became more scared and supported the military spending (and they made a lot of money on it as well). Of course later events and documents came to prove them wrong on their assertions.
'Neo-conservatism' began with these people under Nixon, challenging Kissinger and more conventional foreign policy.
That 'Team B' was a bureacratic device created with the purpose of countering the CIA's estimates of lower risk from the Soviet Union, to protect and increase military budgets. It was 'outside experts' - approved by the new CIA Director, wait for it, George H. W. Bush. Bush wasn't just a CIA director - he had been appointed at a time of the greatest crisis in the agency's history, just after Congressional hearings, with some cooperation from the CIA Director who was telling some truths, exposed all kinds of out of control operations.
Bush had proven his total political loyalty already - at a time no Republican wanted to be the Chair of the Republican Party during Watergate where they'd be forced to defend the administration, Bush had accepted the assignment - and when they needed someone who would keep the secrets and be totally politically loyal against efforts to reign in the CIA, they appointed Bush again.
Of course, when Reagan was elected, they were back in power - now with Bush as VP - and it was a very ugly period in our history, as Iran was mysteriously friendly with the Reagan administration (where it was found we were illegally selling them weapons), where we were sponsoring and training death squads in Central America who were killing thousands of people like labor leaders to support right-wing dictatorships (these are the 'raped and killed the nuns and killed the Arch-Bishop) people, where Congress had outlawed any money for Contras in Nicaragua but these interests were using money from everywhere from those Iranian Arms deals to apparently skimming from cocaine smugglers to illegally fund the Contras, a group of former secret police and criminals who Reagan called "the moral equivalent of our founding fathers"), when partially exposed leaving Reagan to tell the nation that 'his heart said his administration had not traded arms for hostages, but his head said the evidence showed they had'. Dark days of hidden, and often evil, security state activities.
These are the same interests who helped push America into the first war with Iraq - including with the misleading of the American people and Congress, a moving factor being the testimony of a woman who spoke of Saddam's troops in Kuwait who were taking babies out of hospital incubators... except the woman was lying, and the daughter of the ambassadors from Kuwait which was not known at the time, her remarks part of a PR campaign designed by a major US PR company, with the office who did it headed by Bush's former Chief of Staff... but the same motives for oil and power in the region and positioning the US for any future military activities existed then as well...
(Funny enough, it was the same people involved in tensions then, as Colin Powell backed off simply executing masses of Iraqi troops as they fled back to Iraq).
Under Clinton, these same people wrote a letter to Clinton pressuring him to renew the war in Iraq, under their new organization, 'the Project for a New American Century'...
The arguments they made for war - whatever bits of truth are in them, what parts are propaganda, they shed a bit of light on the best case they could come up with, they're historical documents now from that PNAC organization - funny enough, George W. Bush was advised to let Cheney pick his VP, and Cheney did a search and selected himself, and Bush's foreign policy and military appointments were right from the PNAC membership.
So there's a lot of history of these interests that had wanted that war for their own combination of reasons, and were in a position to push them under Bush as figurehead.
Their influence is shown by how, within hours of 9/11 Bush was telling the shocked people who weren't part of the neocons, to find a connection to Saddam that didn't exist.
That even was hijacked by these people to justify the war - nothing more to it.
To summarize my point here - there are existing 'security interest' officials, the neocon establishment largely, who had this agenda for war as one major factor.
2. I don't think Bush was 'owned' by these people - but he was their willing enabler generally. There were moments he did not support them - notably after the 2006 elections Democrats won where he replaced Rumsfeld (days after promising Rumsfeld had his full support). Bush had other reasons in addition to the neocon agenda listed above.
One large reason was, as Bush had confided earlier, that he understood that 'a war president is a lot more powerful'.
Not only did he want that power - he had come into power viewed as a weak candidate, the spoiled son of a previous president who was a sort of party boy with little to qualify him and he'd lost the popular vote and the election had, as many Americans knew, been stolen - he wanted to strengthen his position. He wanted to be a war president.
And he was right about the politics - these war incidents, on 9/11 and when he invaded Iraq - provided massive increases in his public support and ended talk of the stolen election.
A media constortium had done a recount of Florida votes showing Gore had won, but the results came in soon after 9/11 and the media mostly hid them.
This simple desire to be a 'war president' for more power - with Iraq the best choice of where to do it (early in his administration there seemed to have been some misguided efforts to stir up 'war with China' sentiments that were abandoned after 9/11) - appears to have aligned him well with wanting war with Iraq.
3. Some have speculated about some motive to 'beat his father', by getting Saddam where his father had backed off of that.
I have no information to support that - it seems very speculative to me. It may have provided him some satisfaction and further interest - I don't know how much.
But I don't place much weight on it.
4. Little known history about the Iraq war is that the US had massivve plans for rebuilding Iraq for a right-wing agenda.
An entire set of economic policies that were a right-wing economist's fantasy playground - starting with a flat tax but incuding much more - were laid out secretly. We already had our new leader of Iraq in the wings ready to fly in and put in his puppet position - Chalabi. It was a plan for country by people who knew nothing about how to build a country but had plenty of right-wing policies waiting to be pushed. Of course the plans fell apart when the expected short war went badly with years of strong resistance.
The State Department - under Colin Powell - had created a detailed plan for occupying Iraq and building it back.
But Cheney and Rumsfeld had persuaded Bush to move control for the occupation from the State Department to Rumsfeld and State's plan was thrown away.
But these right-wing interests who expected to use Iraq as a laboratory and model for their policies was a motive at the time of pushing the war.
5. The thing we know was not really a factor was the reason they actually gave, WMD.
In a shockingly honest confession, Wolfowitz wrote an article and admitted that the process had been that they met to discuss how best to sell the war to Congress and the public, "For bureaucratic reasons we settled on one issue, weapons of mass destruction, because it was the one reason everyone could agree on."
So this goes to show that while they were all aligned for war, this same debate looking for a reason and justification led to finding a hyped up WMD 'threat'.
It wasn't that they didn't TRY to also lie about a link between Saddam and 9/11 - they did - but WMD was more effective.
Another reason to use WMD was the fact that the UN Charter prohibits a member from starting a war - with an exception for 'pre-emptive war' meaning that if another nation has massed forces on your border and is clearly about to attack - the word is 'imminent' - you can attack them first - and the Bush administration claimed there was such an 'imminent threat' of attack by Saddam against the US, to claim it was following the charter.
This is were fantasies of things like crop dusters hired by Saddam to spread anthrax came from.
6. Oil. Now, I am not well enough informed to say a lot about just how the oil agenda works. It's not as simple as 'they have oil and we're going to take it'. That has been the case at times; the CIA's first covert operation was about Iranian oil, when there was a deal to buy their oil cheap under pressure, and the new government wanted a better deal for their country, England asked the US to help them and we did by overthrowing democracy and putting the Shah in power with a brutal secret police force we supplied to keep him in power. What could go wrong? But by the time of Iraq, the situation was a lot more complicated with oil.
One tidbit we do have, as I mentioned, is that Cheney's primary priority early in the Bush administration was chairing a secretive energy policy review - and a lawsuit managed to get a few documents from it released, and those documents were maps of Iraq's oil fields, that's how they spent their time on US energy policy. One issue is simply 'friendly control' of oil that is a strategic resources for our competitors such as China, who Saddam would be happy to sell to.
It's also a fact that in the chaotic post-war period, as ever government agency was looted and destroyed (not to mention the museums), one building was protected by US forces under Rumsfeld's policy - the oil ministry. And oh by the way, when Chalabi was derailed as the leader of Iraq - he was put in charge of the oil ministry.
Was it a coincidence that the initial name the government selected for the Iraq war effort was Operation Iraq Liberation - OIL - before the media caught on and they changed it?
7. There's the whole 'the defense industry profits hugely from war' issue. Hard to say just how much that played a role, but seems very likely it was one supporting factor.
Nevermind the direct relationships between people such as Cheney with Halliburton who stood to profit enormously, it's a large interest of the Republican party.
8. Strategic positioning for further control in the Middle East, i.e., war with Iran.
Look at a map, and Iran is surrounded by US allies now. Iraq has a lot of value as a base for US miliary forces for use in the region - including a base for war with Iran.
This partly falls under the PNAC agenda, which well understood that value.
Returning to PNAC for a moment, one of the factors they mentioned was that US power was well servied by periodically attacking and showing military dominance - doesn't matter the enemy, just attack somoene from time to time to make a point. That's the sort of morality - and agenda they admitted - they have.
I'm sure I've missed some things, and there's no way to say how much weight each had - the bottom line was Bush needing to say he's in favor of war, and all these helped.
Edit: one I forgot:
9. A replacement for our bases in Saudi Arabia
In 1990 after Saddam invaded Kuwait, we put US bases in Saudi Arabia. This had the backing of the Saudi government, but outraged many Muslims because Saudi Arabia is the home of their religion, where Mecca is located. It would be a bit like China putting military bases in Vatican City for Catholics. As USA Today reported in 2003:
During his interview with Vanity Fair in early May, Wolfowitz cited several payoffs from the war, including removing the need for American forces in Saudi Arabia.
Those troops were sent to protect the desert kingdom against Saddam, whose forces invaded Kuwait in 1990. But their presence in the country that is home to Islam's holiest sites enraged many Muslims, including al-Qaeda leader Osama bin Laden.
Within two weeks of the fall of Baghdad, the United States announced it was removing most of its 5,000 troops from Saudi Arabia.
"Their presence there over the last 12 years has been a source of enormous difficulty for a friendly government," Wolfowitz said. "It's been a huge recruiting device for al-Qaeda."
Funny thing is, Osama bin Laden 'got what he wanted' with that policy and 9/11.
Now, it's my opinion that bin Laden's agenda was not accurately reflected in the reasons he gave for 9/11; the reasons he gave were propaganda aimed to sell his attack to the Muslim world.
Suddenly, bin Laden was concerned about the Palestinians, for example.
But bin Laden's religious outrage over the bases in Saudi Arabia does seem sincere; his turn to radicalism largely came when he asked Saudi Arabi to let him drive our Saddam instead of the US, and they turned him down. It's a bit ironic that - good idea or not - the 9/11 attack did lead us to get rid of those bases.
I have to suspect the Saudi government was pressuring us to get rid of them.
I suspect it's just one more factor that made it seem like a good idea to go to war in Iraq.