In 1793, he became Wayne's aide-de-camp and learned how to command an army on the American frontier; he participated in Wayne's decisive victory at the Battle of Fallen Timbers on August 20, 1794, which ended the Northwest Indian War. Harrison was a signatory of the Treaty of Greenville (1795) as witness to Wayne, the principal negotiator for the U.S. Under the terms of the treaty, a coalition of Indians ceded a portion of their lands to the federal government, opening two-thirds of Ohio to settlement.Following his mother's death in 1793, Harrison inherited a portion of his family's Virginia estate, including approximately 3,000 acres (12 km2) of land and several slaves. He was serving in the Army at the time and sold his land to his brother.Harrison was promoted to Captain in May 1797 and resigned from the Army on 1 June 1798.