Mid-1940?
Axis victory.
An estimated 3+ million German troops were in the Eastern Front at the start of Operation Barbarossa. This meant that the majority of the German troops were fighting the Russians specifically by the end of the war. Take the Eastern Front away from the Germans, and the Axis would have one of the strongest land armies ever known. No part of Allied Europe would have been able to stop such a force, and Eurasia would be impenetrable from the Western Front.
The Axis now has:
- a much stronger army
- better and more artillery
- more resources
- a country on its side with previous experience of allying with members of the Allied Powers
The Soviets could teach Germany the most modern methods of mass production learned from the US, offering huge quantities of raw resources and food, granting access to the world’s most expansive intelligence operations. Meanwhile, Germany could offer advanced technologies and military expertise. During the actual war, one advantage that Britain had over Germany was a great deal of colonies to pull resources from, while Germany was starved of them. Assuming the Soviet Union joined the Axis, that advantage wouldn’t exist anymore for Britain for two reasons:
- The Soviet Union has a good deal of resources it could feed Germany in this scenario. Germany would have much more oil and grain, and that would have allowed for it to wage war much more effectively.
- The Soviet Union would be powerful enough to be able to effectively take over British colonies and grab resources from them, as well as help Italy and Germany do the same.
Britain’s position in the Middle-East would have been gone in no time. The Soviets would take Persia, Iraq, and the rest of the Middle-East up to the Suez (no more oil shortage for the Axis from that point on-wards). The British would be forced to pull out of Egypt and Greece due to the closing of the Suez canal. Italy would also be able to occupy Egypt and link up with Italian troops in Ethiopia that are already there. The U.K. would surrender after Spain gives Axis transit rights to Spanish-Morocco and Allies lose possession of both its Middle-East and North African possessions. By this point, Germany would very heavily increase U-Boat production and research of missiles.
If not that, the Soviets and Nazis would be fighting the British troops in Africa or Western Europe, and the sheer manpower from the Axis army would have crushed them (literally and figuratively) either way. The Allied Invasion of Sicily would also have been much harder to achieve with actual success. With that front gone too, the Western Front could not have been opened because of the number of enemies surrounding them as a result of Germany not fighting a two-front war.
By this point, Britain would be colonised, and the rest of Mainland Europe would be split between the Axis Powers. Central Asia would become primarily Soviet territory. Japan would have successfully taken East China, and Southeast Asia up to Oceania, where Australia and New Zealand would eventually be Japanese colonies too.
Either way, the only real way the Allies could have won would be if America joined the war, developed the atomic bomb first and used it on a major Russian or German city.