Where the golden rule in military causality ratio comes from?

WWII losses of various countries (lazily from https://en.wikipedia.org/wiki/World_War_II_casualties):
France: 210,000 Killed : 390,000 Wounded
Germany: 5 million Killed : 7.3 million Wounded
Hungary: 200K K : 90K W
Italy: 320K K : 275K W
Japan: 2.2M K : 326K W
Polan: 240K K : 766K W
Romania: 300K K : 330K W
SU: 10M K : 14.5M W
UK: 383K K : 376K W
US. 407K K : 671K W

Korean War (Wikipee, not including missing and deadly wounds and such):
RoK: 137K K : 450K W
US: 33K K : 103K W