Ok, so I realize this is likely a concept that has been done-to-death. But I recently took it upon myself to start writing a WW2 TL, and besides, a fresh look on the scenario has a lot of potential, no?
1939 - 1940; The Beginning of the War that changed the World
September - December; 1939
Europe
It started in September. On the first of the month, at 4:45 AM, Nazi Germany begins its invasion of Poland, as the Luftwaffe enter the country in order to bomb strategic city targets. Soon after, by 8:00 AM, Nazi land forces enter the country, near the town of Mokra.
This does not go unnoticed by France and the United Kingdom however, who promptly issue ultimatums against the Third Reich, preparing for war. Soon to follow, Australia, New Zealand, Canada, Newfoundland, South Africa and India also declare war on the Reich. But the tide was soon to change.
To the surprise of many, the USSR began its own invasion of Poland on the 17th, Soviet troops entering the country from the East. The minor offensives by the French and the British against Germany all but grind to a halt as commanders gawk in shock at the new found alliance between Stalin and Hitler.
In the short war, the Polish military is crushed between the skilled troops of the Third Reich and the sheer mass of the Soviet army. Poland is partitioned along the river Wisla, with Hitler's Germany gaining a land corridor to the formerly free state of Danzig, and a portion of the border facing the Slovak Republic.
The great powers of Europe as of yet make no great move against Nazi Germany, or the USSR as Stalin begins to bully the lesser powers of North Eastern Europe.
By December, Poland is fully partitioned by both Germany and the USSR, Western Poland becoming a direct part of the Third Reich, and Eastern Poland being annexed by the SRs of Belorussia and the Ukraine. As the month draws to a close, Soviet troops enter Finland, looking to secure the country against a possible beach-head by the growing number of enemies.
The Soviets make little gains against the Finns in the advent of the Winter War, the Finns making absolute destructive use of captured Soviet weapons and vehicles, grinding the Soviet forces to all-but-a-halt, but the sheer mass of Soviet troops continues to push them forward.
Asia
Japan continues its encroaching into mainland China, as well as scattered border skirmishes against the USSR. While the border-war beteen the USSR and Japan has not yet ended, skirmishes begin to decrease in severity, alluding to a coming end to the conflict.
Japanese-Russian tensions flare up once more after a Soviet Officer (one of the few to escape the purge), is accidentally killed by Japanese Artillery fire. The Soviets begin increasing the troops stationed in Japan, drawing more away from the European front, due to the peace secured with Hitler.
Fully armed warfare begins between the states of Mongolia and Manchuria, obviously backed by their respective powers. While no truly formal war has been sparked between Japan and the USSR as of yet, the gun is still waiting with its trigger ready to be pulled.
In mid-December, Japan and the USSR declare war on each other "in support" of their respective puppet-states. Japanese land troops clash with Soviet troops in Manchuria, and elements of the Japanese Navy assail the Eastern Russian coast. Japanese advance in China slows, as troops are called away to support the Russian front
