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The United States did not emerge with its current borders fully formed. From its independence in 1783 through the mid-20th century, Washington expanded its territory through a combination of purchases, treaties, wars and annexations, steadily extending its reach across North America and into the Caribbean and Pacific.
These acquisitions, driven at different times by security concerns, economic opportunity and geopolitical rivalry, reshaped the country’s map and its role in the world. Below is a chronological look at how the United States acquired its territory, and what each expansion meant.
Treaty of Paris (1783)
Britain formally recognised US independence and ceded land east of the Mississippi river. This defined the borders of the new nation after the Revolutionary War.
Vermont annexation (1791)
The independent Vermont Republic joined the United States as the 14th State. It was the first territorial expansion after independence.
Louisiana purchase (1803)
The US bought a vast territory from France for $15 million, doubling its size. The deal secured control of the Mississippi river and fueled westward expansion.
West Florida annexation (1810)
The US claimed parts of Spanish West Florida following a local uprising. It strengthened American control along the Gulf Coast.
Florida acquisition (1819)
Spain ceded Florida to the US under the Adams-Onís Treaty. In return, Washington dropped its claims over Texas.
Texas annexation (1845)
The Republic of Texas was admitted into the United States as a State. The move heightened tensions with Mexico and led to war.
Oregon territory settlement (1846)
The US and Britain peacefully divided the Oregon Country at the 49th parallel. This avoided war and secured the US access to the Pacific Northwest.
Mexican cession (1848)
After the Mexican-American war, Mexico ceded large parts of the Southwest. The US paid $15 million, gaining California and vast western lands.
Alaska purchase (1867)
The US bought Alaska from Russia for $7.2 million. Once mocked, the deal later proved valuable for resources and strategy.
Hawaii annexation (1898)
The US annexed Hawaii after overthrowing its queen. It became a State in 1959 and a major Pacific hub.
Panama Canal Zone (1903)
The US gained control of the Canal Zone to build and operate the canal. The territory was returned to Panama in 1999.
Guantanamo Bay lease (1903)
The US secured a permanent lease for a naval base in Cuba. The arrangement remains in place despite Cuban objections.
Water Island (1944)
The US purchased Water Island from a private Danish company. It was later added to the US Virgin Islands.
Pacific Trust Territories (1947 onwards)
The US administered former Japanese-held islands under a UN mandate.
Some later became independent nations; others remain US territories.