American fear of too big losses eliminates them as potential Mandalorians.
Americans are also too hypocritical: they hide their brutality behind the veil of hollywood sweet propaganda and present themselves as peaceful nation which they aren't (they're still living on lands belonging to slained indians BTW)
Only Germans with their noble cult of war, their prussian discipline and ordnung, their focus on conquest are similar to Mandalorians. And Germans are descendants
of ancient germanic tribes that ruined decadent Rome. Wehrmacht in WWII was ultra-disciplined army: even in Russia german soldiers weren't stealing and raping
women in a contrary to US savages in Iraq - craddle of human civilization.