"Whatever their publicized angst over Saddam Hussein's 'weapons of mass destruction,' American and British authorities were also concerned about violence in an area that harbors a resource indispensable for the functioning of the world economy," Greenspan wrote.
"I'm saddened that it is politically inconvenient to acknowledge what everyone knows: The Iraq war is largely about oil," added Greenspan, who for decades had been one of the most respected U.S. voices on fiscal policies.
"I think that it's really about stability in the Gulf. It's about rogue regimes trying to develop weapons of mass destruction. It's about aggressive dictators," Gates said.
"After all, Saddam Hussein launched wars against several of his neighbors," Gates said. "He was trying to develop weapons of mass destruction, certainly when we went in, in 1991."
Gates's defense came a day after thousands of anti-war protesters marched in Washington. A spokeswoman for one of the groups who organized the march said more than 200 protesters were taken into custody, including at least 10 Iraq war veterans, when they attempted to cross a police barrier near the U.S. Capitol.