7 Westward Expansion and Manifest Destiny
Trace how U.S. territorial growth in the nineteenth century reshaped migration, Indigenous and Mexican communities, and the national conflict over slavery.
Territorial growth and its justifications
During the nineteenth century, the United States expanded across the continent through purchases, treaties, annexation, and war. was a belief popular among many white Americans in the 1840s that the United States was destined to spread across North America. Supporters used it to justify expansion, while motives also included access to farmland, trade, resources, and Pacific ports.
Expansion was neither inevitable nor peaceful. Governments made decisions about territorial growth, and people already living in lands claimed by the United States resisted or were displaced.
Major territorial changes
1803, : The United States bought a vast territory from France, extending its claims west of the Mississippi River.
1845, annexation of Texas: Texas had declared independence from Mexico in 1836. Its annexation by the United States contributed to a border dispute and war with Mexico.
1846, Oregon Treaty: The United States and Great Britain settled competing claims to Oregon Country, setting much of their boundary at the 49th parallel.
1848, : At the end of the Mexican-American War, Mexico ceded a large area to the United States, including present-day California and much of the Southwest. The treaty recognized the Rio Grande as the Texas boundary, and the United States paid Mexico $15 million.
1853, Gadsden Purchase: The United States bought additional land from Mexico in what is now southern Arizona and New Mexico.
Migration and the people affected
People moved west to farm, trade, seek work, join family, or pursue opportunities such as the California Gold Rush. Overland routes, including the Oregon and California trails, carried migrants from eastern starting points across the plains and mountains. The journeys were difficult and dangerous, and settlement brought profound change to the regions migrants entered.
These lands were not empty. Indigenous nations had longstanding communities, governments, economies, and relationships to their homelands. U.S. expansion and settlement frequently led to warfare, treaty pressure, land loss, and forced relocation. The of 1830 enabled the federal government to pursue the removal of Native nations from lands desired by settlers, and many people were forcibly driven west. Indigenous resistance and survival continued throughout the period.
Expansion also transformed life for people of Mexican descent. After the Mexican-American War, residents of the ceded territories came under U.S. rule. Although the addressed citizenship and property rights, the transfer of sovereignty and subsequent settlement brought political and economic pressures, and many Mexican landholders lost property.
Territorial expansion and slavery
Each new territory raised the divisive question of whether slavery would be permitted there. The answer could shift the balance between free and slave states in the Senate and affect the future power of slaveholders.
In 1820, the attempted to contain the dispute by admitting Missouri as a slave state and Maine as a free state. It restricted slavery in much of the remaining north of latitude .
Territory acquired from Mexico reopened the conflict. The admitted California as a free state while allowing the status of slavery in Utah and New Mexico to be decided locally. It also included a stronger Fugitive Slave Act.
In 1854, the allowed settlers in those territories to decide the slavery question through and repealed the restriction. Proslavery and antislavery settlers rushed into Kansas, and violence followed.
Growing national divisions
Territorial growth connected disputes over land and migration with Indigenous sovereignty, the rights of Mexican residents, slavery, and political representation. Each new territory revived conflict over slavery and the balance of power between free and slave states.
Repeated compromises failed to resolve the conflict over slavery’s expansion. Rather than settling national divisions, expansion intensified them and brought the country closer to civil war.