Why America Invaded Iraq

Why did America invade Iraq in 2003? Was it for oil? Or was it because Saddam Hussein was a mass-murdering dictator who harbored terrorists and threatened the region with Weapons of Mass Destruction? If it was the former, wouldn't it have been a lot easier to just buy Iraq's oil on the open market? And if it was the latter, why did Hillary Clinton, Joe Biden and John Kerry support President Bush? Noted British historian, Andrew Roberts, has the answers.