And where is "elsewhere"? Has this mysterious "elsewhere" also recently fought two long, overseas wars this century?
Current American opposition to war has a lot to do with the fact that the country has been in a state of war essentially for the entire 21st century, in locations very far away from home soil.
Basically this.
In my own words the whole question is kind of silly considering the United States during the ACW suffered casualties and industrial/economic losses which in that century could only be compared to the the entirety of the Napoleonic Wars or the Taiping Rebellion in China. The only reason the whole idea of 'war weariness' set in during the ACW was that to many it seemed as though the war would just drag on forever, and three years of draft, fighting, and destruction takes its toll on any nation no matter how strong.
The US, as proved by many conflicts, has never been incredibly casualty averse, at worst I'd say that the American public has always been averse to 'mission creep' since Vietnam, but that's the most you could say.