Until the US developed the atomic bomb, Nazi Germany was the deadliest most advanced military in the world.In WW I the combine British and French forces were able to fight the outnumbered Germans to a stalemate. The big unpleasant surprise in WW II was how quickly France fell. The Germans simply went around the Maginot Line. That left Britain to face Germany alone.
https://en.wikipedia.org/wiki/Maginot_Line
The other small European countries were no match for Germany however fierce resistance by the Greeks delayed Germany's invasion by a month. The rest is history.