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The United States quadrupled its territory in six decades through a sequence of purchases, treaties, and wars the FSOT expects you to name precisely. The Louisiana Purchase (1803), negotiated by Robert Livingston and James Monroe for roughly $15 million, doubled the national domain and forced Thomas Jefferson—a strict constructionist—to concede that the Constitution contained no express power to acquire territory, which he justified under the treaty power. The Adams-Onís Treaty (1819) secured Florida from Spain and fixed the transcontinental boundary to the Pacific. The annexation of Texas (1845) by joint resolution under President John Tyler precipitated the Mexican-American War (1846-1848), concluded by the Treaty of Guadalupe Hidalgo (February 2, 1848), which transferred the Mexican Cession—California, Nevada, Utah, and parts of Arizona, New Mexico, Colorado, and Wyoming—for $15 million and assumption of claims. The Oregon Treaty (1846) with Britain set the 49th parallel boundary, and the Gadsden Purchase (1853) added the southern strip of Arizona and New Mexico for a rail route.
The phrase "Manifest Destiny" was coined by journalist John L. O'Sullivan in the Democratic Review in 1845, asserting the nation's God-given right "to overspread the continent allotted by Providence for the free development of our yearly multiplying millions." The doctrine fused Protestant providentialism, Jacksonian democracy, and Anglo-Saxon racial ideology. It rationalized the displacement of Mexicans and Native nations and justified the annexationist program of the Polk administration.
Federal land policy engineered settlement. The Northwest Ordinance (1787) had established the template: survey, territorial government, then statehood on equal footing. The Homestead Act (1862) granted 160 acres to settlers who improved the land for five years; the Pacific Railway Acts (1862, 1864) chartered the Union Pacific and Central Pacific, whose lines met at Promontory Summit, Utah, on May 10, 1869, binding the continent and accelerating the destruction of the bison economy. The Morrill Land-Grant Act (1862) endowed agricultural colleges from public land.
Expansion was never politically neutral. Each acquisition reopened the question of slavery's extension: the Missouri Compromise (1820), the Wilmot Proviso (1846), the Compromise of 1850, and the Kansas-Nebraska Act (1854) all turned on whether new territory would be slave or free. Frederick Jackson Turner's "Frontier Thesis" (1893), delivered after the Census Bureau declared the frontier closed in 1890, argued that the frontier had forged American democracy and individualism—a thesis the FSOT may test as historiography, not settled fact.
The FSOT treats Native American policy as a continuous federal program with identifiable statutory and judicial landmarks. The foundational case is Johnson v. M'Intosh (1823), in which Chief Justice Marshall articulated the "discovery doctrine," holding that European discovery gave the discovering sovereign exclusive title and reduced tribes to a right of occupancy. The Indian Removal Act (1830), signed by Andrew Jackson, authorized the exchange of eastern tribal lands for territory west of the Mississippi.
In Cherokee Nation v. Georgia (1831), Marshall described tribes as "domestic dependent nations" in a relationship to the United States resembling "that of a ward to his guardian." In Worcester v. Georgia (1832), the Court held that Georgia law had no force within Cherokee territory, recognizing tribal sovereignty. Jackson reportedly defied the ruling; enforcement never came. The result was the Trail of Tears (1838-1839), the forced removal of the Cherokee along with the other "Five Civilized Tribes," killing roughly 4,000 of some 16,000 Cherokee.
Westward settlement collided with Plains nations. The Sand Creek Massacre (1864), the Sioux War culminating in the Battle of the Little Bighorn (June 25, 1876), where Lt. Col. George Custer's 7th Cavalry was destroyed by Lakota and Cheyenne under Sitting Bull and Crazy Horse, and the Wounded Knee Massacre (December 29, 1890), which killed roughly 250-300 Lakota and closed the era of armed resistance, are the dated instances to retain. Congress ended treaty-making with tribes by statute in 1871.
The Dawes Severalty Act (1887) broke up communal reservations into individual allotments (160 acres per household head), declaring "surplus" land open to white settlement; tribal landholdings fell from about 138 million acres in 1887 to 48 million by 1934. The policy aimed at forced assimilation, reinforced by off-reservation boarding schools such as Carlisle (founded 1879), whose motto "Kill the Indian, save the man" captured the era's logic. The pendulum reversed only with the Indian Reorganization Act (1934) under John Collier, which ended allotment and restored a measure of self-government, and citizenship was extended to all Native Americans by the Indian Citizenship Act (1924).