Complex sentence: He fought in the Duke of Wellington's army then returned to America to serve in the War of 1812 as an infantry captain in the United States Army where served in the 41st Infantry Regiment from 1 August 1813 to 15 June 1815.
Split into simpler sentences: He fought in the Duke of Wellington's army then returned to America to serve in the War of 1812 as an infantry captain in the United States Army. He served in the 41st Infantry Regiment from 1 August 1813 to 15 June 1815.