Westward Expansion (1790-1861)

Searching for new lands and protection from foreign invasion, the young nation quickly extended its external borders.

In 1803, Jefferson negotiated the Louisiana Purchase with France. This covered the area around New Orleans that was already inhabited and the largely unexplored lands to the west of the Mississippi. With this acquisition, the United States doubled in size and made claim to its extension across the continental.

In 1818, a treaty with Great Britain established a new frontier as far as the Rocky Mountains, along the 49th parallel and provided for shared control over the Oregon Territory.   

In the South, the United States annexed the coastal area to the east of the Mississippi and entered into negotiations with Spain for the purchase of Florida.

The Adams-Onis Treaty also marked out the frontier between the Spanish possessions and those of the United States from the Gulf of Mexico to the Pacific Ocean.

Towards the mid 19th century, the statement of ‘Manifest Destiny’ provided a justification for further territorial expansion.

In the north, an agreement was reached with the United Kingdom in 1846 on the division of the Oregon Territory along 49th parallel.

In the south, Texas was brought into the Union; the Guadalupe Hidalgo Treaty brought an end to the Mexican War and led to the integration of huge territories in New Mexico and California.

The last minor acquisition was the Gadsden Purchase, which incorporated the southern part of New Mexico in 1853.

While these moves to push back the international borders, these new territories gradually obtained statement within the Union.

In 1790, there were 13 states, by 1821, this number had increased to 24, and to 34 in 1861.