Here's a principal reason America has historically relied on drawing its military forces from the citizenry, rather than maintaining a standing army. According to a Zogby poll of our mercenaries in Iraq--what else are they?--have been kept in the dark about their mission.
"One surprising finding in the poll is that 85 percent of those surveyed believe that the US's main mission in Iraq is to retaliate against Saddam Hussein for his role in the Sept. 11, 2001, attacks. Numerous commissions and studies have been unable to find that Iraq played any role in the 9/11 bombings. Meanwhile, 93 percent said that they did not think that removing weapons of mass destruction was the reason they were in Iraq."
Amazing, right? Something to keep in mind when you listen to Bush/Cheney and Rummie and his generals talk about the war: They've lied to the troops, they keep lying to the troops, and so there's no reason to believe they're not lying to us.