Complex sentence: Upon the formation of the Imperial Japanese Army in 1871, Hasegawa enlisted as a captain and later, as a major, was given command of a regiment during the Satsuma Rebellion seeing action at the relief of Kumamoto Castle on 14 April 1877.
Split into simpler sentences: Upon the formation of the Imperial Japanese Army in 1871, Hasegawa was commissioned a captain. Later, as a major, he was given command of a regiment during the Satsuma Rebellion, and saw action at the relief of Kumamoto Castle on 14 April 1877.