but retained ownership of their lands, while the Proclamation of 1763 prohibited colonial settlement west of the Appalachians, a grievance that contributed to the outbreak of the American Revolutionary War. The territory was ceded in 1783 to the new American government, who encouraged its citizens to settle in the region and ignored the rights of local inhabitants. In response, the tribes formed the Northwestern Confederacy which from 1786 to 1795 fought against the U.S. in the Northwest Indian War, with military support provided by British forts along the Maumee River. After the 1794 Jay Treaty, the British handed over these strongpoints to the U.S., most notably Fort Detroit, and abandoned their indigenous allies, who signed the 1795 Treaty of Greenville with the American government. Under the treaty, they ceded most of what is now the state of Ohio but granted title to the rest of their lands in perpetuity, a commitment the U.S. government had already secretly agreed to ignore. A key factor in this policy was the acquisition by France of the Louisiana Territory in 1800, which meant the U.S. faced an expansionist power on its northwestern border, rather than a weak Spain. To ensure control of the Upper Mississippi River, President Thomas Jefferson incorporated the region into the Indiana Territory, which originally contained the modern states of Indiana, Illinois, Michigan, and Wisconsin. He appointed William Henry Harrison as governor, ordering him to acquire as much land as possible beyond the Greenville line, using deception if needed. In doing so, Harrison was helped by vague and competing claims, since tribes whose title to the lands was either limited or disputed were happy to sign them away in return for bribes. Although the December 1803 Louisiana Purchase ended the French threat, between 1803 and 1805 he obtained extensive territorial cessions in the treaties of Fort Wayne (1803), St Louis, Vincennes and Grouseland. The policies adopted by Harrison meant low-level conflict between local tribes and American settlers quickly escalated post-1803. In 1805, a Shawnee leader named Tenskwatawa launched a nativist religious movement that rejected American culture and values, while his elder brother Tecumseh organized a new confederacy to defend their territory against settler encroachment. They established a community at Prophetstown in 1808, gaining support from young warriors and traditional chiefs including the Wyandot leader Roundhead and Main Poc from the Potawatomi. The Sioux, Sauk, Meskwaki, and Ojibwe peoples, who lived along