Well, just considering the numbers here........
The sheer number of Germans alone, with TANKS, and Japanese, you know, those suicidal guys that would wake you up in the middle of the night and yell TENNOHEIKA, BANZAI!? yeah, they are kinda gonna be doing that..
Also, Kar-98k, mounted 8x scope, easy one shot bullet through the brain
And i dont think they can simply apparate into Berlin to shoot Hitler, or apparate into Tokyo to shoot Tojo, Hirohito, and the entire Japanese military board.........
There are ALOT of guns within 10 feet of those guys, not to mention Hitler having a Walther PPK
Also, taking out the local commander wouldnt work, as all orders came from Berling or Tokyo, respectively, major reason they lost the war