佐賀の乱
In 1873, Yamakawa was commissioned a major in the Imperial Japanese Army and assigned to the garrison at Kumamoto. In 1874, he fought to suppress the Saga Rebellion and was wounded. Promoted to lieutenant colonel, he was in combat against Saigo Takamori in the 1877 Satsuma Rebellion as a staff officer of the 2nd Independent Brigade. He was trapped in Kumamoto Castle by Satsuma forces, and in the battle saved the life of Tani Tateki. For his actions, he received the Order of the Rising Sun, 4th class in 1878 and he was promoted to colonel in 1880, and in 1888 to major general. However, soon after this promotion, he resigned his commission and entered into the army reserves.