Siberian Intervention
Yamasaki was a native of what is now part of Tsuru, Yamanashi, where his father was a Buddhist priest. He graduated from the 25th class of the Imperial Japanese Army Academy in 1913, and served in the Siberian Intervention from April 1918 to December 1920. In May 1928, he was part of the Japanese expeditionary force to mainland China during the Jinan Incident.