The Allies, after seeing the German military in action, decide to call off any sort of offense. Poland falls mere weeks later, as Communists continue to gain power in Eastern Europe.
Then, the Germans march into Austria in early 1939. The Allies were outraged and immediately send troops to Austria to help. France launches an invasion into Germany as well, keeping it preoccupied. The Soviet Union sends backup, but faces its own problems as Imperial Japan moves in.
Germany orders a massive draft and boosts its manufacturing output. It could easily overcome either France or Auatria by itself, but focusing on one would leave the other in a key opportunity to invade.