US because of the bomb
Since shortly after or sometime durting WW2.
The US has been the most powerful military nation since WW2 (1945).
Thus far in history, I'd say the atom bombs of WW2.
Major Audie Murphy is generally considered to be the most decorated U.S. combat soldier in WW2 since WW2 until Lt. Colonel Matt Urban was considered to be the most decorated U.S. combat soldier and officer, ww2 in 1980 when he was awarded the Medal of Honor and some other prevously recommended decorations for WW2 --"The Matt urban Story", 1989.
When the US didnt negotiate for peace after Pearl Harbor
The British. They managed to outnumber all other countries during the WW2
WW2 was the end of British dominance in the world. The US became the world's most powerful force during and after WW2. Britain has generally followed the US's lead.
Japan is one of the most industrialized and wealthiest countries since WW2
Germany
Switzerland
germany
because after ww2 ended it lead to the cold war