Complex sentence: Alongside his twin brother, Sir John James Hood Gordon, Thomas entered the army, joining the 29th Regiment of Foot on 21st August, 1849, and served in the Indian Mutiny campaign of 1857-1858.
Split into simpler sentences: Alongside his twin brother, Sir John James Hood Gordon, Thomas entered the army, joining the 29th Regiment of Foot on 21st August, 1849. He served in the Indian Mutiny campaign of 1857-1858.