In 1803, President Thomas Jefferson purchased over 800,000 square miles from Napoleon of France for $15 million. This very large section of land stretched from the Mississippi River to the Rocky Mountains and doubled the size of the United States. Jefferson then sent Lewis and Clark on a military expedition to explore the new territory.

President Thomas Jefferson purchased the Louisiana Territory in 1803 from France, thus doubling the size of the United States. Jefferson then sent a military expedition led by Meriwether Lewis and William Clark to explore the new territory (1803-1806). Their goal was to find a water route to the Pacific Ocean, map out the territory, gather scientific information, and establish friendly relations with the natives. With the help of a French fur trapper and his Native American wife Sacagawea, Lewis and Clark could accomplish their goals and return with valuable scientific information in their journals.

In 1818, General Andrew Jackson was sent to defend Georgia against attacks by Seminole Indians from Florida. Already established as a war hero after his success at the Battle of New Orleans in the War of 1812, Jackson led over 3,000 troops to Georgia and pursued the Seminoles into Florida Territory which was owned by Spain at the time. While this was a dangerous move, Spain decided not to go to war over the invasion because of internal problems at home and because it was already fighting with Latin American rebels who were seeking independence from Spain. Instead Spain agreed to the Adams –Onis Treaty of 1821. This treaty ceded (gave up) the Florida Territory to the U.S. in return for the U.S. agreeing to pay Spain $5 million. The treaty also recognized Spain’s sovereignty over Texas.

During the 19th century, Manifest Destiny was the philosophy or idea that it was the destiny of the U.S. to expand its territory all the way to the west coast (“from sea to shining sea”). Using new technology, such as steamboats, canal building, and railroads developed during the Transportation Revolution and the Industrial Revolution, Americans set their sights on the West.

Oregon Territory was a region west of the Rocky Mountains that included present-day Oregon, Washington, Idaho, and parts of Wyoming, Montana, and western Canada. Four different countries claimed the Oregon Territory: the U.S., Great Britain, Spain, and Russia. However, by the 1820s only British and American claims continued. Many settlers were drawn to the territory (“Oregon fever”), and in 1818, Great Britain and the U.S. agreed to jointly occupy Oregon Territory. By the 1840s, many Americans had moved into the territory, traveling by covered wagons along the Oregon Trail, and began calling for an end to Britain’s occupation. During his 1844 presidential campaign, President James K. Polk supported the occupation of Oregon territory. Polk’s supporters adopted the slogan “54°40” or Fight!” (Meaning the U.S. should occupy Oregon Territory to the 54°40’’ parallel). In 1846 President Polk was successful in negotiating a treaty with Britain that established a new boundary at the 49th parallel.

Under the leadership of Joseph Smith, Jr., the Church of Jesus Christ of Latter Day Saints (Mormons) established several settlements between 1830 and 1840s in Ohio, Missouri and Illinois. Mormons were persecuted (harassed) for their beliefs. Joseph Smith, Jr. was later murdered by an angry mob in 1844 in Illinois. After Smith’s death, most Mormons found a new leader in Brigham Young. To escape persecution, the Mormons traveled across the Great Plains and Rocky Mountains. From 1846-1869, 70,000 Mormons travelled to Utah Territory and established communities (including present-day Salt Lake City). The journey is called the Mormon Trail which covered over 1,300 miles. The Mormons made many contributions to the region. The growth of Mormon communities helped to spread agriculture to the West. Population growth in the region would eventually help lead to statehood. The Mormon Trail contributed to westward expansion and the fulfillment of Manifest Destiny.

The United States tried to purchase Texas from Mexico in 1827 and again in 1829, but both times Mexico refused to sell. In the 1830s, northern opponents of slavery argued that making Texas part of the U.S. was a southern effort to extend slavery to the Southwest. In 1844, President John Tyler presented the U.S. Senate with a proposed treaty to annex Texas, but the Senate overwhelmingly defeated the proposed treaty. Toward the end of his presidency, President Tyler once more tried to accomplish Texas’ annexation but this time by a joint resolution of Congress rather than by a treaty. The newly-elected, incoming President, James K. Polk, was persuaded to accept Congress’ joint resolution annexing Texas. The Texas Legislature, the voters of Texas, and both houses of the U.S. Congress approved annexation, and Texas became the 28th state on December 29, 1845.

In the 1840’s Mexico and the United States went to war over some disputed territory. Mexico claimed the Nueces River as its border, and the U.S. claimed the Rio Grande River as its border. When fighting broke out, U.S. President James K. Polk enticed Americans into war by claiming, “Mexico shed American blood on American soil!” The United States defeated Mexico and signed the Treaty of Guadalupe Hidalgo in 1848, thus gaining a vast amount of land in the Southwest known as the Mexican Cession and expanding the United States to the Pacific coast.

Gold was discovered in 1848 in California by accident at Sutter’s Mill which was owned by John Sutter. In 1849, news of the gold discovery spread quickly, and thousands of Americans, along with people from all over the world, rushed to California. By the end of 1849, this newcomer population was estimated at 100,000 compared with a pre-1848 population of less than 1,000. These fortune-seekers became known as the Forty-Niners. Even though few of these Forty-Niners actually struck it rich, miners did extract, it is estimated, more than 750,000 pounds of gold. The Gold Rush peaked in 1852. Many of the Forty –Niners stayed in California and took up farming or started businesses after the “gold fever” had died out. This enormous population boom had several effects on the territory. Gold mining towns such as San Francisco sprung up. California soon applied to become a state and joined the United States, under the Compromise of 1850, as a free state.

After the Mexican-American War and the Mexican Cession (land given to the U.S. in 1848 in the Treaty of Guadalupe Hidalgo), the U.S. Government, purchased a portion of Mexican land (29, 670 square miles) for $10 million in what is part of present-day Arizona and New Mexico. This treaty is known as the Gadsden Purchase, after James Gadsden the U.S. Minister to Mexico. The U.S. purchased the land in 1854 in order to complete a transcontinental railroad. With the Gadsden Purchase, many Americans felt their dream of Manifest Destiny was fulfilled.