Many Japanese felt participation in WWI had benefitted their country.
In 1919, Japan was given former German possessions in China and a Mandate over the German Pacific island possessions that the Japanese navy had taken.
The war industry thrived and Japan’s niche in the Asian market grew while European countries were engaged in the war. Despite increasing conflict between labor and management and a vocal political left at home, the Empire of Japan was euphoric. They had been victorious in war, and increased the span of their empire with little cost.
Japanese book “SHOWA Day by Day Vol.3” published by Kodansha; Wiki Media Commons.