After the first world war the USA became the most powerful one.
Hmmm. The atomic bomb, the German 88 flak gun, and the tiger tank.
The United States emerged from World War II as the richest, most powerful nation on Earth.
The most powerful was the IS-2 Josef Stalin. The one with the most longevity was the Centurion (and also the most capable at the onset of WW2). The best to have seen significant service in the majority of the war was arguably the Panther.
For modern rifles I think it's a 60 cal it was an anti tank rifle in world war one or two. On google search modern firearms anti tank rifles and that website has it on there
Britain.
germany
Propaganda.
the tank
the T-34 tank.
hitler and stalin
The Atomic bomb.