Complex sentence: By that time, Colt had become one of the wealthiest men in America was presiding over his enterprise from Armsmear, an ornate Italianate manor built near the armory in 1857.
Split into simpler sentences: By that time, Colt had become one of the wealthiest men in America. He was presiding over his enterprise from Armsmear, an ornate Italianate manor built near the armory in 1857.