From a longtime e-friend:

Americans don’t do ruthless well, never have (except maybe for Southerners like Nathan Bedford Forrest). One of the reasons for the huge Federal Government propaganda efforts on the home front in both World Wars was the knowledge by Wilson and Roosevelt and those in their Administrations that without a constant barrage of pro-War propaganda, the American people would turn against the War — particularly after the casualties began coming home and the next-of-kin started getting visits from military officers. It was that very unwillingness of the American people to support a war which led Japan to attack Pearl Harbor — giving the Roosevelt Administration “Remember Pearl Harbor!” as a rallying cry and tag line for a whole lot of anti-Japanese propaganda which some today have said is racist, but which is simply the material the Administration decided would best keep the American people behind the war effort. Had Hitler not declared War on the US, most historians doubt that FDR could have gotten a Declaration of War against Germany through Congress. Perhaps its the historically short national attention span which causes the drop in support for wars unless constantly motivated by pro-war propaganda. Little pro-war propaganda was produced during Korea. And none during Vietnam. And none now. History has shown that relying on the opposition press to keep the public on the pro-war side doesn’t work. You’ve seen the caricatures of Lincoln which filled opposition newspapers during the Civil War. The pro-Lincoln, pro-war press had to turn up the volume to compete. Greeley’s famous willingness to give up in 1864 was what, allegedly, led to the falling out between him and Whitelaw Reid. I’ve read descriptions of American “atrocities” during Korea and Vietnam and, unless the describers are deliberately playing down what took place, the Germans and the Russians and the Koreans and the Chinese and the Japanese all were much more nasty in committing atrocities than the Americans. (Have you seen the pictures of Japanese soldiers using Chinese babies for bayonet practice during the rape of Nanjing? [tossing their little bodies back and forth bayonet to bayonet?])