Dark Grey is the Stahlpakt and Pink is the Entente Réelle.
The Soviet Union invaded Eastern Poland on September 1st 1939 as per the Molotov-Ribbentrop pact, banking on Western non-intervention given Germany's successful taking of Czechoslovakia and Danzig. What followed was a joint declaration of war on the Soviet Union by both Britain and France, and soon after by Finland.
After this development, Germany immediately dropped the Molotov-Ribbentrop pact and declared war on the Soviet Union as well, and began an invasion of Poland without a formal declaration of war to "protect Poland from collapse." This move angered the Entente, but they were unwilling to declare war on Germany after having already commenced hostilities with the Soviet Union. The Entente attacked from British influenced Persia and from Finland, as well as via several landings on the Arctic Sea coast in a retread of the Entente intervention in the Russian Civil War decades earlier. The Axis invaded overland into the heart of Russia.
In 1942 the Metz Conference was held between the Entente and the Axis, concerning the post war European political order. The independence of a free Poland was insisted upon, and Germany relented on the condition that it be allowed to annex Polish lands that were once part of the German Empire and West Galicia, which was once part of Austria. The Soviet Union was to be dismembered to once and forever remove the threat of Russian and Bolshevik aggression. The partition plan called for a rump Russian state, an enlarged Ukraine, Belarus and Finland, a Turkestan consisting of the various Central Asian SSRs, a Ural state, and a state in Southern Russia and the Caucasus. Crimea was to annexed into the German Reich directly. Population exchanges were to occur bloodlessly and in good order. The Rump Russia was to be divided into French, British, German and Italian occupation zones to oversee disarmament and debolshevikisation prior to the release of a strictly neutral Russia. Moscow, within the German sector, was to be split between the Entente and the Axis as well for administrative purposes.
Belarusian and Ukrainian nation states were justified by retroactively naming Ukrainians and Belarussians as partially Aryan through the Eastern Goths and the Varagians, albeit Aryans that have been Russified and in need of "spiritual cleansing." Additionally the Nazis retroactively modified their war goals from annexing everything up to the Urals to merely achieving dominion over much of the continent so that the Volk would have all the resources it would need to thrive. Prior concepts of literal living space were mostly abandoned.
The two parties also begrudgingly agreed to spheres of influence. Much of continental Europe was to fall into the Axis Sphere, something the Entente couldn't seriously oppose when the axis possessed roughly 4 times as many divisions. In particular the Entente had to recognize German influence in Poland, a country that was wholly occupied by Germany by 1942, lest they just annex it outright.
The Second Great War ended in 1943, shortly after German troops entered Moscow. The Entente and Axis troops occupied their respective zones.
The Germans consolidated control over their bloc, while falling short of Hitler's vision of a continent spanning Reich, Poland and the former Soviet territories were forced to sign treaties that allowed German economic penetration, offered various extraterritorial privileges to Germans living within their borders and to collaborate with the murder of their nations' Jewish population. A series of post war conferences redrew the map within the Axis Zone, to the condemnation of the Entente.
The occupations zones in Russia soon became hard borders, with South Russia becoming a German client state and North Russia becoming a constitutional Republic. North Moscow became a North Russian exclave surrounded by Axis territory. Plans for the enlargement for Finland were abandoned as the Entente focus shifted to building North Russia into a strong ally against the Axis.
Hitler died in 1953 of drug complication. What followed was a period of De-Hitlerisation by the new Fuhrer Rudolf Hess, who introduced a series of reforms, most notably officially announcing the Final Solution complete and ending the extermination of what little Jews remained in Axis Europe.
The Cold War between the Entente and the Axis show no signs of stopping though, and by the 1950s both blocs gained access to nuclear weapons and satellite technology.