Engaging Russia (Eastern Front), while starting the attack on England (Western Front), Greatest mistake was fighting a war on two fronts.
Invading Russia too early.
Usually "Operation Barbarossa", or the German invasion of the Soviet Union, is considered to be Hitler's biggest mistake.
yes he made a great mistake in throwing a war against USSR.
Invasion of the USSR was Hitler's biggest mistake.
Many historians believe that Hitler was overconfident of the German Army's abilities. The invasion of Soviet Union was the biggest mistake Hitler made as Britain and the USA were able to 'attack from behind'. Hitler seemed to believe that Germans were somehow endowed with superhuman powers, this misguided belief led him to make strategic errors.
Yes it was, It costed 80% of Germany's entire army.
Hitler made no mistakes but he only broked several agreements in the Treaty of Versailles.
Hitler himself was a mistake
Napoleon made the same mistake of thinking that invading Russia was easy. Both Napoleon and Hitler learned the error of their ways - don't mess with Russia. The vast area, the extremely cold winters, the resolve of the Russian people to throw every man, woman and child into the effort to beat off invaders, made Russia a step too far.
Based on my knowledge, Joseph Stalin's greatest mistake was to trust Adolf Hitler by sending a representative to sign the Non-aggression Pact on May 15, 1941.
There may be different opinions on this, but IMO the biggest mistake Russia made was making the Molotov-Ribbentrop Non-Aggression Pact of August 1939. This was an agreement between Hitler and Stalin that neither would invade the other. Hitler had plans all along to violate the pact, but in signing the pact, Russia was fell asleep at the wheel (so to speak). When Hitler invaded, Russia was pushed back all the way to Stalingrad.
He launched an invasion (codenamed Operation Barbarossa) into the Soviet Union. Many historians suggest that it was the largest mistake Hitler had made - he dedicated too many supplies and troops to Operation Barbarossa when he could've used that same man power to invade Great Britain (which would've given him a stronger foothold in the Atlantic).