Complex sentence: After the war with Mexico ended, Porter returned to West Point and became a cavalry and artillery instructor from 1849 to 1853, and then became adjutant to the academy's superintendent until 1855.
Split into simpler sentences: After the war with Mexico ended, Porter returned to West Point and became a cavalry and artillery instructor from 1849 to 1853. He served as adjutant to the academy's superintendent until 1855.