Emperor Yoshihito became head of state of Japan in 1912. Japan used the terms of the alliance signed with Britain in 1902 to declared war on Germany on 29th August,1914. Emperor Yoshihito ordered the seizure all the Chinese ports controlled by Germany and with the help of Britain captured the German Pacific Islands. Japan also extended its control of Manchuria and in 1918 attempts were made to occupy Siberia.
Japan gave some assistance protecting British shipping convoys in the Far East. The Japanese Navy was also involved in the allied hunt for German surface raiders in the Pacific.
Wages in Japan were kept low during the war and a 400% wartime rise in rice prices provoked rural food riots in July 1918. The riots spread to more than 30 provinces but came to an end when they were ruthlessly suppressed by the government. There were over 10,000 arrests and a large number of executions.
Article 156 of the Treaty of Versailles transferred to Japan all German State submarine cables in China. Japan also gained control of the German colony of Kiachow although they had to promise they would eventually return the territory to China.