Britain had ceded land extending as far west as the Mississippi River in the Treaty of Paris of 1783. Following adoption of the Land Ordinance of 1785, American settlers began freely moving west across the Allegheny Mountains and into the Native American-occupied lands beyond. As they did, they encountered unyielding and often violent resistance from a confederation of tribes. After taking office, Washington directed the Army to enforce American sovereignty over the region. Brigadier General Josiah Harmar launched a major offensive against the Shawnee and Miami Indians in the Harmar Campaign, but was repulsed by the Native Americans. Determined to avenge the defeat, the president ordered Major General Arthur St. Clair to mount a more vigorous effort. St. Clair's poorly trained force was almost annihilated by a force of 2,000 warriors led by Little Turtle, Blue Jacket, and Tecumseh.