insurgency, n. an insurrection against an existing government, usually one’s won, by a group not recognized as having the status of a belligerent.
resistance, n. an underground organization composed of groups of private individuals working as an opposition force in a conquered country to overthrow the occupying power, usually by acts of sabotage, guerrilla warfare, etc.: the resistance during the German occupation in World War II.
The term resistance is the more correct because we are, in fact, an occupying power. But the Bush administration has ordered the media to use the term insurgency because it paints as legitimate the current government in Iraq. Hence, with each usage we are left with the frame: What's wrong with those people over there, why are they trying to destroy everything? Don't they know we are only there to help their government in helping them? And the American public becomes a bit more disconnected from reality.
*Republicans' two-decade-old "perception management" strategy [which] became official policy during Ronald Reagan's first term. On Jan. 14, 1983, President Reagan formally initiated the strategy by signing classified National Security Decision Directive 77. At the time, the White House worried that a repeat of Vietnam-type anti-war sentiment might constrain U.S. foreign policy in Central America and elsewhere. Also known as “public diplomacy,” the project had a more overt side that sought to build support for U.S. policy abroad, but it also had a less-visible domestic component that targeted the American people and the press. Robert Parry Secrecy & Privilege: Rise of the Bush Dynasty from Watergate to Iraq.