The Americans entered the area when Robert Gray sailed up the Columbia River in 1792. The first American overland excursion into Oregon was made by the Corps of Discovery in 1804–1806. Dispatched by Thomas Jefferson to explore the lands of the Louisiana Purchase and beyond, Captains Meriwether Lewis and William Clark and their party of 30 men and one woman, Sacagawea, trekked across the continent to the mouth of the Columbia, camped south of present-day Astoria during the winter of 1805–1806, and then returned to St. Louis.

Lewis and Clark’s exploration and mapping of Oregon threw down the gauntlet for future settlement and eventual annexation of the Oregon Territory by the United States. The expedition also initially secured good relations with the Native Americans in the West, thus establishing the preconditions to trade and the missionary influx.

Following Lewis and Clark’s journey, there were years of wrangling over the right of the United States to settle in the new territory. The mere threat of British gunboats on the Columbia caused the quick departure of American John Jacob Astor’s Pacific Fur Company during the War of 1812. It wasn’t until the Convention of 1818 that the country west of the Rockies, south of Russian America, and north of Spanish America was open for use by American citizens as well as British subjects.

During the 1820s, the Hudson’s Bay Company continued to hold sway over Oregon country by means of Fort Vancouver, on the north shore of the Columbia. More than 500 people settled here under the charismatic leadership of John McLoughlin, who oversaw the planting of crops and the raising of livestock. Despite the establishment of almost half a dozen Hudson’s Bay outposts, several factors presaged the inevitable demise of British influence in Oregon.

Most obvious was the decline of the fur trade as well as Britain’s difficulty in maintaining her far-flung empire. Less apparent but equally influential was the lack of white women in a land populated predominantly by white trappers and explorers. If the Americans could attract settlers of both genders, they’d be in a position to create an expanding population base that could dominate the region.

The first step in this process was the arrival of missionaries. In 1834, Methodist soul-seekers led by Jason Lee settled near the Willamette River. Four years later, another mission was started in the eastern Columbia River Gorge. In 1843, Marcus and Narcissa Whitman’s missions started up on the upper Columbia in present-day Walla Walla, Washington (until 1853, the Washington area was considered a single entity with Oregon). The missionaries brought alien ways and diseases for which the Native Americans had no immunity. As if this weren’t enough to provoke a violent reaction, the Native Americans would soon have their homelands inundated by thousands of settlers lured by government land giveaways.