What would happen if starting 1945, after seeing the Holocaust, the United States embarks an absolute, zero tolerance to any war crimes, genocides, atrocities, or violations of the Geneva Convention, with or without world consent? This also means refugee crisis and any large scale humanitarian crisis. The US response can be as mundane as sending aid to total military intervention.
Would this change the way the colonial powers handled their colonies and the progression of decolonization?
How would this effect the way the Cold War was handled?
Could the USSR coexist with a USA of this fashion without nuclear war?
What effects would this have on the world?
What would today look like?