UK was a naval empire; that meant that a very long standoff between Germany and UK was possible; checking that France was not ready to an invasion through Belgium was possible. So there were reasons to believe that crushing France would work, and neither UK nor Germany had any reason to be sure about the loss in the standoff.
As for USSR, well, his blitz attack worked exceptionally well. Germany didn’t have material advantage on the 20th June; it did on the 22nd June. Also it had a well-trained army. Actually, a regime with fascist ideology with less stress on nationalism to the point of extermination (like in Italy) had a chance to win the war against USSR with such a tactics...
UK was a naval empire; that meant that a very long standoff between Germany and UK was possible; checking that France was not ready to an invasion through Belgium was possible. So there were reasons to believe that crushing France would work, and neither UK nor Germany had any reason to be sure about the loss in the standoff.
As for USSR, well, his blitz attack worked exceptionally well. Germany didn’t have material advantage on the 20th June; it did on the 22nd June. Also it had a well-trained army. Actually, a regime with fascist ideology with less stress on nationalism to the point of extermination (like in Italy) had a chance to win the war against USSR with such a tactics...