Complex sentence: He joined the Army as an Ensign in the 2nd Foot Guards (Coldstream Guards) in 1768, was promoted to lieutenant and captain (1775) and to lieutenant-cololonel in 1780.
Split into simpler sentences: He joined the Army as an Ensign in the 2nd Foot Guards (Coldstream Guards) in 1768. He was promoted to lieutenant and captain in 1775 and to lieutenant-colonel in 1780.