Prior to the arrival of Europeans, Oregon was well populated with Indian tribes. Coastal Indians harvested the bounty of the sea and seashore. Other tribes inhabited the Willamette Valley, Eastern and Southern Oregon. Although the first Europeans to sight Oregon were probably Spanish sailors, the first serious exploration was accomplished by British expeditions led by James Cook, and George Vancouver. American claims were reinforced by the Lewis and Clark Expedition. By 1825, Russian and Spanish claims to the territory were given up by treaties. Britain and the United States could not agree on a line between their respective claims, so they agreed to allow the citizens of both countries to settle. The Hudson's Bay Company had a trading post at Fort Vancouver at the present site of Vancouver, Washington, on the north side of the Columbia River. American missionaries established the first permanent white settlements in the Willamette Valley at Salem. With the opening of the Oregon Trail in 1843, the population of settlers grew rapidly and pressure to settle the border question grew. In 1846, a treaty designated the 49th parallel as the boundary, which placed the present states of both Washington and Oregon in the United States. The Oregon territory was organized in 1843 and statehood was achieved in 1859. Numerous wars between settlers and Indians were fought during the 19th century. During the Modoc War of 1872 and 1873, a small band of Indians used hideouts across the border in California to hold down more than 1,000 soldiers. One of the most famous conflicts was the Nez Percé War. The Nez Percé resisted attempts to move them from their homeland in the Wallowas of northeast Oregon to a reservation in Idaho. They were led by Chief Joseph on a long march that ended in surrender near the Canadian border. In the first decade of the 20th century, Oregon voters adopted initiative, referendum, and recall procedures to give more power to the voters. Collectively, those provisions became known as the Oregon System.