Thanks for the replies.
Why did the USA pressuring the Japanese to leave Siberia? They were not at all friendly with the USSR?
There was a Red Menace but there was also a Yellow Peril. Indeed, to many Americans, the latter was the greater threat (especially since it was widely thought that Bolshevism could not last long):
"As the Wilson era ended in 1920-1921, U.S.–Japan relations reached their nadir. As in 1906 and 1913, anti-Japanese moves by Californians provoked outrage in Japan and a war scare. This time, however, the situation was more dangerous. Washington and Tokyo were at loggerheads over Shantung, Siberia, and the Anglo–Japanese Alliance—which Americans saw as giving cover to Japanese aggression. Moreover, the two nations were now locked in a naval race. In 1916, the United States embarked on a massive naval building program, and three years later shifted much of its growing fleet to the Pacific. In 1920, Japan responded in kind by undertaking a naval buildup of its own.
"Heightened tensions with Japan gave rise to a new wave of Yellow Peril books such as Frederick McCormick's
The Menace of Japan (1917) and Sidney Osborne's
The New Japanese Peril (1921). These writers argued that Japan's growing military and naval power and ongoing absorption of China and Siberia made it even more dangerous, increasing the likelihood of a Pacific war and a Japanese invasion of Hawaii and the West Coast. Hollywood jumped on the bandwagon by releasing in 1917 the Hearst-financed film
Patria, which depicted Japanese troops, aided by Mexicans and Japanese-American fifth columnists, overrunning California in an orgy of rape, murder, and looting.
"The Japan-as-Yellow Peril image was meanwhile updated. Rather than being seen merely as semi-Westernized warriors, they were now pictured as "Prussianized" ones. As a State Department official put it in 1919, "the spirit of Japan is that of Prussia, whom the Japanese leaders openly admire and whose government they chose for a model.". Valentine McClatchy, a prominent California exclusionist, helped to popularize this notion in his influential 1920 tract The Germany of Asia. McClatchy professed to admire the Japanese as a people. The problem, he claimed, was their adoption of "militaristic" German models and methods, which had led them to embark on a "relentless and implacable" campaign of imperial expansion at China's and America's expense. Senator Henry Cabot Lodge, chairman of the Foreign Relations Committee, was more blunt: Japan, he declared in 1919, was the "Prussia of the Far East" and the "coming danger of the world.""
https://books.google.com/books?id=uN1XAwAAQBAJ&pg=PA46