I think in the aftermath of the fall of the Soviet Union, a lot of people (neo-conservatives in particular) got a little arrogant about US power (see for example
The End of History). The think tank
PNAC gathered likeminded neo-conservatives together and was eventually hugely influential in the Bush Administration.
And, to be fair to Cheney and Rumsfeld, they weren't crazy for wanting to get rid of Saddam. If they could've gathered a wider coalition and had a better plan for post-Saddam Iraq, they probably wouldn't have quite the negative reputation they have today.
