Complex sentence: During the early 1780s Cooper became a storekeeper in Burlington, New Jersey, and by the end of the decade he was a successful land speculator and wealthy frontier developer in what is now Otsego County, New York.
Split into simpler sentences: During the early 1780s, Cooper became a storekeeper in Burlington, New Jersey. By the end of the decade, he was a successful land speculator and wealthy frontier developer in what is now Otsego County, New York.