Complex sentence: Hamilton was the Colonel of the 15th Regiment of Foot from 22 August 1792 to 1794 before becoming Colonel of his old 21st Regiment of Foot from 1794 to 1803.
Split into simpler sentences: Hamilton was the Colonel of the 15th Regiment of Foot from 22 August 1792 to 1794. He became Colonel of his old 21st Regiment of Foot from 1794 to 1803.