I suppose capital-intensive and labor-intensive wars may have quite different psychological impacts on combatants.
But let's not forget that the main reason Washington may not directly kill a million in Iraq, Afghanistan, etc. is that the wars in which it did kill more than a million civilians each -- the Korean and Vietnam Wars -- were unpopular; the latter eventually became so unpopular that Washington had to abolish conscription, which made it capable of fighting only relatively smallish wars and reluctant to subject US soldiers to too much combat (force protection is more important than fighting insurgents to death, so retreat to bases and train locals to do the fighting).
On 30 April 1975, the Vietnamese Communists finally triumphed. Whatever the rest of the world think of subsequent history of Viet Nam (or whether they think about it at all), Iraqis, Afghans, Iranians, Venezuelans, Americans, all of us should thank the Vietnamese for rendering Americans unwilling to fight any big wars that cause millions of casualties.
-- Yoshie <http://montages.blogspot.com/> <http://mrzine.org> <http://monthlyreview.org/>