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President Thomas Jefferson finalizes the purchase of the Louisiana Territory from France for $15 million. This monumental deal doubles the size of the United States. It opens vast new lands for exploration, farming, and settlement—and challenges the government to organize and govern its expanding domain. -
The Corps of Discovery, led by Meriwether Lewis and William Clark, departs from St. Louis to explore the newly acquired Louisiana Territory. Over two years and four months (until 09/23/1806), they chart rivers, record new species, and build alliances with Native tribes. Their journey reaches the Pacific Ocean and returns vital maps that guide future westward migration. -
The United States declares war on Great Britain over trade restrictions and British support of Native resistance. Lasting until 12/24/1814, the war ends in a stalemate but strengthens U.S. independence and national pride. With British influence removed from the frontier, westward migration and settlement accelerate. -
Congress passes the Missouri Compromise to balance slave and free states. Missouri enters as a slave state, Maine as a free state, and slavery is banned north of latitude 36°30′ in future territories. This law temporarily maintains political balance but deepens sectional divisions that will later erupt into civil war. -
President Andrew Jackson signs legislation authorizing the forced relocation of Native American tribes living east of the Mississippi River to lands west of it. Between 1831 and 1850, thousands of Cherokee, Creek, Chickasaw, Choctaw, and Seminole people were driven from their homes. Many perish on the brutal marches known as the Trail of Tears. -
The first large wagon train sets out from Independence, Missouri, headed for the fertile lands of Oregon. Over the next two decades, more than 400,000 settlers follow this 2,000-mile route, enduring disease, river crossings, and harsh terrain. The Oregon Trail becomes a symbol of Manifest Destiny and the American frontier spirit. -
After declaring independence from Mexico in 1836, the Republic of Texas officially becomes the 28th U.S. state. Its annexation angers Mexico, which still claims the territory, leading directly to the outbreak of the Mexican–American War the following year. -
The first clash between Mexican and U.S. troops occurs along the Rio Grande. The war ends with the signing of the Treaty of Guadalupe 02/02/1848. Mexico cedes vast territories—including California, Nevada, Utah, and parts of Arizona, New Mexico, and Colorado—cementing U.S. expansion “from sea to shining sea.” -
James W. Marshall discovers gold at Sutter’s Mill in Coloma, California. Word spreads rapidly, triggering a massive migration known as the “Forty-Niners.” Between 1848 and 1855, hundreds of thousands of people pour into California, transforming it into a booming, diverse, and chaotic frontier that joins the Union in 1850. -
President Abraham Lincoln signs the Homestead Act, granting 160 acres of free land to settlers who agree to live on and cultivate it for at least five years. This law encourages thousands of families to move west, transforming the Great Plains into farmland and expanding U.S. settlement across the continent. -
The Union Pacific and Central Pacific Railroads meet at Promontory Summit, Utah to mark the first rail connection between the Atlantic and Pacific coasts. The railroad revolutionizes travel and trade, links distant regions of the nation, and accelerates both economic growth and Native displacement in the West.