Complex sentence: After he retired from active military service in 1923, declining promotion to Field Marshal, he returned to his native island of Shikoku and became the principal of the Hokuyō Junior High School (present-day Matsuyama High School).
Split into simpler sentences: After he retired from active military service in 1923, declining promotion to Field Marshal. He returned to his native island of Shikoku and became the principal of the Hokuyō Junior High School (present-day Matsuyama High School).