This alternate timeline details what might of happened if Imperial Japan never joined the Axis alongside Nazi Germany and Fascist Italy.
Point Of Divergence
Although Japan had already taken Manchuria as a puppet regime, the Japan and Chinese hostilities didn't truly break out until the Invasion of 1937. This sparked the 2nd Sino-Jap War, at it is here that the divergence occurs.
In this timeline, before the Nanking Massacre can occur, the Japanese forces decide to push into the Lake Kashan one year early. Thus in November, the Japanese met both Chinese and Soviet resistance, along with defeat. By December, Josef Stalin had ordered the STAVKA, a dangerous armed forces group, to begin preparing counterplans against the Japanese Empire. In the original timeline, the United States condemns the actions of Imperial Japan, generally based on the Nanking Massacre. But because the awful ordeal never takes place, the US sees the Sino-Jap war as the the forefront to a communist alliance between China and the Soviet Union.
Indeed it becomes one, for with the early Soviet aid, China begins to push Japan back. By February of 1938, the Soviet-Chinese forces successfully defeat the invading Japanese. They retreat back to their island nation. The US sees these events unfold, and immediately increases the amount of trade between the two nations. In the original timeline, the US begins to place embargoes on Japan, withholding oil and other necessary goods. But in this reality, the US builds up the amount of goods, seeing Japan as the foothold against the spread of Communism in Asia.
Because of the increased relations between the US and Japan, the French Indochina incident, along with Panay doesn't happen. Soon the friendliness between the US/Japan completely hinders the Empire's need to invade other lands for raw materials. But this increased the animosity between China and their new ally, the Soviet Union. Stalin saw the growing dangers in the pacific, so he launched more Soviet forces into China. What started as allies, became hostile overlords, as Russia overtook China with military control. This swift takeover was carried out by the forces of Mao Zedong's communist faction. By 1939, The Soviet Union had absorbed China under its long arm of control, along with retaking Manchuria as a puppet regime. Because of their brutal dominance, a Nanking-sort of Massacre occurs between the months of April-June, 1939.
Japan and the US saw this carnage, and immediately begin building plans against the Soviet Union, now doubled in size with the overtaking of China, Mongolia, Nepal, and parts of Bangladesh, Bhutan, and Myanmar. Empowered by this massive new territory taken as part of the Soviet Union, Josef Stalin entered into talks with Nazi Germany. Seeing as the though the two nations have polar opposite ideologies, they both share the will to dominate. On August, 1939, Stalin and Hitler meet in Stalingrad to discuss as sort of pact between the strong nations, in a plot to spearhead a global invasion, and dividing the conquered lands between them. Eventually as the talks longed into early September, Hitler had Benito Mussolini enter the fold, as he represented Italy in this new pact. The nations then declared on September 5th, that the nations would live in harmony and alliance, in their bids to conquer. The Axis was formed, and Hitler would be granted Europe, while Russia would get Asia and the Pacific, and lastly Italy would be granted Africa.
After finalizing these peace agreements, Stalin later brought up the threat of US incursion in Soviet affairs, given their growing alliance with Japan, whom Stalin vehemently detests. Hitler and Mussolini thought about this as well. Once the agreement was settled, and the leaders returned to begin their plans, they agreed to form a mutual committee of advisors from all three nations. Their job would be to devise a proper plan, in which the Axis could agree on how to invade and defeat the United States, if it came to such a task. The committee would have to prepare prototype invasion plans, that the trio of dictators could revise and adapt, while also coming up with a way to equally divide up the United States, (along with nations North and South of the border), between Germany, Italy, and Russia.