How is it that with all the Wars the US has fought, why are there so many Germans & Japanese etc in America?

The US is and since the later part of WW2 has been the worlds foremost Military might and has paid this price, the price of freedom dearly, Omaha beach to Okinowa, why is it that after such bloody battles, for instance the Coral Sea that the US fosters even stronger ties with those they have defeated to the point where they seem to forget about the War Crimes the Japanese etc...committed and seem to imilate them openly into US culture as one ? Also why is their such a huge US-Russian population, after the Cold War, or was that already in place long before hand ?