I think a lot of the Bush folks thought of Saddam as a kind of rogue asset. They'd funded him to attack the Iranians, and then he went off reservation when he invaded Kuwait, and later tried to assassinate HW Bush. They knew he had chemical weapons (because they had sold them to him), and tricked themselves into believing he was developing nukes. 9/11 ramped up the paranoia and gave the Bush administration license to lie their way into war.
Prior to the Iraq war Saddam was pressing the UN to lift a bunch of sanctions and courting Russian and European oil companies to come in and run their oil operations. By the time of the invasion Iraq's oil infrastructure had been gutted due to sanctions.
This was a complete anathema to the PNAC psychos' vision of the Middle East [0]. They basically wanted to exact control over the majority share of OPEC producers for power over economic rivals (as they saw them).
The PNAC [1] had been pushing for war in the Middle East from their founding in the 90s. They got a lot of buy-in from all the Nixonites in GWB's administration. Rumsfeld set up the Office of Special Plans [2] that stovepiped unvetted intelligence from a bunch of Iraqi expats and exiles to push PNAC narratives to GWB.
The most credible theory in my eyes as to why they needed to invade Iraq, was that Saddam intended to boycott the US dollar, and rather sell Iraq's oil in Euros.
There's a de facto global tacit agreement to sell oil in US dollars - on pain of unilateral sanctions by the US or military intervention by the US military. All countries who deviate from this agreement are in fact deemed enemies of the US. This includes, Iran, Venezuela, Russia and China, and (formely) Iraq and Libya. When they don't, that means that the US can't simply print dollars as they please and force other countries (who purchases that oil) to purchase US debt as well. Pricing oil in currencies other than the worlds reserve currency (the US dollar) affects the dollar value greatly. The US printed about 10 trillion dollars in two years. The rest of the oil-dependent world pays the price.
> There's a de facto global tacit agreement to sell oil in US dollars - on pain of unilateral sanctions by the US or military intervention by the US military.
That is 100% how the US has managed to maintain as a "stable" global currency.
