After the battle of France, Germany did temporarily eliminate the threat of two-front warfare, when germany's enemies on the Western Front were left with only one Britain, and Britain alone was unable to return to the Western Front. Although Britain has an unprecedentedly powerful navy, but in the army is too far behind the German army, even if the British Army can land in Europe under the cover of its navy, but it is impossible to compete with the German Army inland, and at that time the British Air Force had no advantage over the Luftwaffe, and had not yet formed a strong bomber force, on the contrary, in order to resist the German invasion, it was fully producing fighters to strengthen the defense of the mainland. On the whole, Britain had moved to a full range of defenses, germany had taken full control of the Western Front, and the Western Front could not have been opened until at least 1942. It was on the basis of the above strategic background that Hitler issued the order to attack the Soviet Union.
Two-front combat is a taboo for soldiers, and Germany is more deeply aware of this aspect, Germany's defeat in the First World War was caused by two-front combat, Hitler also personally experienced this war, he naturally understood the importance of avoiding two-front combat, it can be said that any German at that time understood that Germany must not fall into a two-front war again. In dealing with the Polish problem, we can see Hitler's efforts to avoid a two-front war, Poland is allied with France and Britain, and Germany is sure to defeat Poland quickly, but it is impossible to predict the duration of the war once the war with Britain and France begins. In order to avoid the Soviet Union eventually taking the side of Britain and France (negotiations had already begun at that time), Hitler took the lead and signed a non-aggression pact with the Soviet Union on the condition of ceding the vital interests of half of Poland's territory, temporarily exempting the threat of war on the Eastern Front and allowing the German army to deal with the Anglo-French coalition forces with all its strength. Although Hitler hated the socialist regime in the Soviet Union, out of national interest, he chose to cooperate with the Soviet Union, and it can even be said that he took the initiative to pander, and the fundamental purpose was to avoid a two-front war.
After the end of the war on the Western Front, Hitler's direct enemy was only one Britain, and the indirect enemy was also a Soviet Union, and in the long run Germany was still in danger of being caught in a two-front war, and Hitler's greatest fear was the alliance between Britain and the Soviet Union. Hitler tried to solve the problem through political means, that is, to reach peace with Britain, but failed, and it could only be solved by military means, after all, there was not much time left for Hitler, from two years to a year. From a military point of view, the only thing that Germany is likely to defeat quickly is the Soviet Union, mainly because the German navy is too weak to ensure that the German Army can safely pass through the English Channel, the Luftwaffe has not been able to seize the key air superiority, and the purpose of direct landing on the British mainland to defeat it is impossible to achieve, and can only blockade Britain through the air force and naval submarine force, and this method is very slow to work, and it is necessary to increase the scale of aircraft and submarine production. According to Hitler, Germany could not vigorously develop its air force and navy while maintaining a strong army.
At that time, the German Army had completed full mobilization, and with two years of european experience, the German Army had reached its peak at that time, and even the powerful French army was rapidly disintegrating under the blows of the German Army, which was previously considered the strongest army on the European continent. Although the Size of the Soviet Army was large, its combat effectiveness was not recognized, and the Russian Army was considered a peasant army from the time of Tsarist Russia, and was not at all an opponent of the German Army in World War I. By the Soviet era, the Western countries did not have a high opinion of the Soviet army, especially in the recent Soviet-Finnish War, the Soviet army still paid a heavy price in the situation of absolute superiority to win the victory. At that time, the German top brass, including the German army generals, had no doubt about defeating the Soviet army militarily, believing that it was entirely feasible to defeat the Soviet army in a few months, and that the battle plan was written by a professional General Staff. According to Hitler's vision, the war against the Soviet Union will be completed within three months, and the German army will occupy the entire western region of the Soviet Union, thus seizing a vast strategic buffer zone and depriving the Soviet Union of the ability to counterattack; and in the three months of fighting against the Soviet Union, Britain on the Western Front will never be able to open a second battlefield, so in Hitler's view, the German army will not fall into the situation of two-front operation, but defeat the Soviet Union can eliminate the danger of two-front operation once and for all, and finally Hitler made up his mind to start a war against the Soviet Union!