Astor took advantage of a treaty called Jay's Treaty between the United Kingdom and the United States in 1794 which opened new markets in Canada and the Great Lakes region at the expense of the Canadians. By 1800 he had amassed nearly a quarter of a million dollars, and had become one of the leading figures in the fur trade. Astor was given permission to trade in ports monopolized by the British East India Company, and greatly benefited from the fur trade with China. He established the American Fur Company on April 6, 1808 headquartered in Astoria, Oregon but this fur trading venture failed when the British captured his trading posts during the War of 1812. A lengthy description based on documents, diaries etc. was given by Washington Irving in his travelogue Astoria.
Astor turned his sights on New York City real estate. At the time of his death, Astor was the wealthiest person in the United States, leaving an estate estimated to be worth 20 million dollars or more.
His eldest son John Jacob Astor II(1791-1869) being insane,the great bulk of this fortune was bequeathed to his second son,William Backhouse Astor Sr