The desecration of the bodies of Japanese soldiers was so common that in 1944, Life magazine published a light-headed photo of a young woman posing with a Japanese soldier’s skull sent to her from New Guinea by her Navy boyfriend. That same year, columnist Drew Pearson reported(pdf) that Representative Francis E. Walter (D-Penn.) had presented President Franklin D. Roosevelt with a letter opener made from the forearm of a Japanese soldier.
I happen not to think that the war in Afghanistan is an imperial war, but more to the point I suspect that the soldiers' behaviour in this case had nothing to do with whether it is imperial or not. Almost every war has its atrocities.
Yes, but long, long wars with constantly recycled and exhausted troops, often acting alone or in small units, is a function of empire. The war in Afghanistan has lasted longer than Vietnam. Americans are not suited for such endless occupations; and they test even the most professional military's discipline and command.
(Photo: On April 30, 1944 Lieutenant (Junior Grade) E. V. McPherson, of Columbus, Ohio with a Japanese skull, which serves as a mascot aboard the United States Navy motor torpedo boat 341. Wikipedia Commons)