Complex sentence: He returned to the United States in February 1805 and became engaged in the "light duty" of shipbuilding activities at Portland, Maine, where he died of a gastrointestinal illness on 25 August 1807.
Split into simpler sentences: He returned to the United States in February 1805 and became engaged in the "light duty" of shipbuilding activities at Portland, Maine. He died in Portland of a gastrointestinal illness on 25 August 1807.