1. Louisiana Purchase:
- Year Territory Acquired: 1803
- Three Key People or Groups: Thomas Jefferson (U.S. President at the time), Napoleon Bonaparte (French Emperor who sold the territory to the U.S.), Meriwether Lewis and William Clark (led the famous Lewis and Clark Expedition)
- Event leading up to becoming part of the U.S.: In 1803, the United States purchased the Louisiana Territory from France for $15 million, doubling the size of the country. The acquisition occurred after negotiations with France, led by Thomas Jefferson, to secure a strategic trade route for the United States along the Mississippi River and access to the important port of New Orleans.
2. Florida:
- Year Territory Acquired: 1819
- Three Key People or Groups: Andrew Jackson (U.S. General in the First Seminole War and eventual President), Adams-OnĂs Treaty (negotiated between the U.S. and Spain), John Quincy Adams (U.S. Secretary of State who played a significant role in the acquisition)
- Event leading up to becoming part of the U.S.: Florida was acquired from Spain through the Adams-OnĂs Treaty of 1819. The treaty settled border disputes between the two countries and provided for the transfer of Florida to the United States. Prior to the treaty, Andrew Jackson led military campaigns in Florida against Native American tribes and Spanish forces, which put pressure on Spain to negotiate.
3. Annexation of Texas:
- Year Territory Acquired: 1845
- Three Key People or Groups: Stephen F. Austin (Father of Texas), Sam Houston (Military and political leader of Texas during the Texas Revolution), James K. Polk (U.S. President who supported the annexation)
- Event leading up to becoming part of the U.S.: Texas was originally part of Mexico, but in 1836, the Texas Revolution resulted in the establishment of the Republic of Texas. After a period of independence, Texas sought annexation to the United States due to ongoing border disputes with Mexico and to secure protection. James K. Polk supported the annexation and Texas became a U.S. state in 1845.
4. Oregon Territory:
- Year Territory Acquired: 1846
- Three Key People or Groups: Lewis and Clark (explorers who explored the region in the early 1800s), John L. O'Sullivan (journalist who popularized the phrase "manifest destiny"), the Oregon Trail pioneers
- Event leading up to becoming part of the U.S.: The Oregon Territory was jointly occupied by the United States and Britain under the Treaty of 1818. However, tension grew between the two countries over territorial claims. In 1846, the Oregon Treaty was signed, establishing the border at the 49th parallel and making the present-day states of Oregon, Washington, and Idaho part of the United States.
5. Mexican Cession:
- Year Territory Acquired: 1848
- Three Key People or Groups: Zachary Taylor (U.S. General in the Mexican-American War), James K. Polk (U.S. President who pushed for the acquisition), Treaty of Guadalupe Hidalgo (ended the Mexican-American War)
- Event leading up to becoming part of the U.S.: The Mexican Cession refers to the land acquired by the United States from Mexico following the Mexican-American War. The war was primarily fought over border disputes between Texas (annexed by the U.S. in 1845) and Mexico. The Treaty of Guadalupe Hidalgo, signed in 1848, ended the war and required Mexico to cede a vast territory that included present-day California, Nevada, Utah, Arizona, New Mexico, and parts of Colorado and Wyoming to the United States.
6. Gadsden Purchase:
- Year Territory Acquired: 1853
- Three Key People or Groups: James Gadsden (American diplomat who negotiated the purchase), Franklin Pierce (U.S. President who supported the purchase), Santa Anna (Mexican President at the time)
- Event leading up to becoming part of the U.S.: The Gadsden Purchase was a small strip of land (present-day southern Arizona and southwestern New Mexico) purchased by the United States from Mexico. The purchase was made to facilitate the construction of a southern transcontinental railroad route. Negotiations led by James Gadsden ultimately resulted in the purchase of the territory in 1853.