150,000 men is hardly a peace corps contingent. The Russians, of course, had a much larger force in Afghanistan with less result that we have in that country, and still have not pacified Czechen despite a much higher butcher's bill than we have paid.
When their mission involves nothing more than "nation-building," "making Iraq safe for democracy," "winning the hearts and minds of the Iraqi people," and serving as targets for IEDs in a simmering civil war, that's exactly what they are.