Hitler launched the German invasion of the Soviet Union on June 22. The fact that the armies were not prepared for a Russian winter show that Hitler did not think that they would still be fighting when winter came. It shows that he thought they would win a quick victory. Hitler was basing this, presumably, on how easily his armies had defeated the Allies in the West. What he was not taking into consideration was how large Russia was in land area and how many Russians there were to fight against his armies. Therefore, he badly underestimated how easy it would be to defeat the Soviets.