Complex sentence: He received a commission as a second lieutenant in the King's Royal Rifle Corps, and served in the trenches in Flanders where he died of a gunshot wound to the head at the age of 21.
Split into simpler sentences: He received a commission as a second lieutenant in the King's Royal Rifle Corps, and served in the trenches in Flanders. He died of a gunshot wound to the head at the age of 21.