How did the various powers stack up militarily in WW2?

by Fire_Bane

I know that the US was the most powerful, and that the Nazis followed closely after, but what about the other powers? How did Britain and the Soviet Union rank on the list? Japan? Italy? Spain?

Georgy_K_Zhukov

Although focused on the US and USSR, this also does touch on Germany and a few mentions of others, so might be of interest.