The Japanese plan to attack central Asia from the territories of Manchukuo and Mengijang is best represented as territorial diffusion.
This type of diffusion occurs when a cultural trait, such as a political ideology or military strategy, spreads from one area to another through the conquest or occupation of territory. In this case, the Japanese military was planning to use its control of Manchuria and Mengjiang to launch an invasion of Siberia.
So, Territorial diffusion is a type of expansion diffusion, which is a broader category of diffusion that includes any type of spread that occurs through the physical movement of people or goods.