Step 3 Resolve Interwar Period
There were a number of conflicts in the interwar period which could change what country controls a specific territory. Most only involved a single territory such as the Rif War or the Indian Independence movement. Territories controlled by the "Split" country must be assigned to a specific country.
There are three conflicts that deserve special consideration, Russian Civil War, Russo-Polish War and the Reunification of China.
Russian Civil War In the context of this scenario generator, it does not matter which side wins as somebody will end up controlling the core Russian areas of Russia, Archangel and Karelia. However there was a possibility of creating a stable country in Siberia controlling multiple areas. Peripheral areas of Russia may gain independence.
Russo-Polish War as closely related to the Russian Civil War. Plausible outcomes range from Russian reconquering Poland to a powerful Polish state controlling Poland, East Poland, Baltic States, Ukraine, East Ukraine and Belorussia. However the outcomes must all involve a contiguous Polish state. Note that even a maximum Polish state remains a minor country.
The order of resolution needs to be
Siberian independence
Peripheral territories status
Russo-Polish War
War of Chinese Reunification By the end of WW1, warlords have already taken control of China. In effect each territory was an independent state. If the Northern Expedition had failed, China would have remained divided.
An additional complication was the Japanese invasion. The Japanese may decide not to invade, to only take Manchuria or to take Kiangsu as well. Note that if the Japan and China end up on the same side, Kiangsu will be returned to China.
Even if China is reunified, there still be independent states formed, representing undefeated warlords or Communist territory. There is also a chance that Kwangtung ends up under effective Chinese control.
In any case the usual China build rules and territory restrictions apply, as the KMT would not even under the best of circumstances had enough time to build a modern industrial economy. If China is allied with Japan, than the movement restrictions are China are lifted.