- The history of the territorial expansion of the United States is a story of wars won and lost, the regions bought and sold. When France lost the French and Indian War in 1763, it ceded most of its possessions in North America to Britain, extending British domain beyond the original 13 colonies. Since Spain was an ally of France, it had to give East and West Florida to Britain. But was compensated by France with territory west of the Mississippi. With the Declaration of Independence from Britain in 1776, the United States was formed from the original 13 colonies but had to wage war with Britain to establish its sovereignty.

The Treaty of Paris concluded the Revolutionary War in 1783, with America expanding to the Mississippi River. And Spain recovering Florida, since in this war it was an American ally. But in 1800, Spain secretly ceded the Louisiana Territory back to France where Napoleon was hoping to establish an empire in North America. When President Thomas Jefferson learned of this arrangement, he became concerned with a potential threat of an aggressive empire builder. He sent envoys to France to purchase New Orleans and West Florida for $10 million. Instead, they came back with the entire Louisiana Territory for $15 million. Napoleon had needed money for his war against Britain.

In 1810, American settlers led a revolt against the Spanish and West Florida, capturing the port of Baton Rouge. The remainder of West Florida was annexed later by President James Madison. In an agreement after the War of 1812, Britain ceded the Red River basin and the boundary between the United States and British territory, what is now Canada, was set at the 49th parallel, with the Oregon territory to be jointly occupied.

In 1821, the Spanish cessions of East and West Florida were finalized. And Spain surrendered any claims to the Pacific Northwest. Later that year Mexico, proclaimed its independence and became another power in North America. Settlers had been moving steadily into Texas and, as in Florida, fought for independence, this time against Mexico.

The Republic of Texas was declared in 1836. The slavery issue had kept Texas from being annexed for several years. But with the threat of a Mexican invasion, President Polk authorized its annexation.

American settlers moved into Oregon Territory, causing border disputes. Rather than risk war in 1846, the border was extended along the 49th parallel as it is today. But to the South, war erupted between Mexico and the United States over the Texas border. Mexico lost and relinquished all claims North of the Rio Grande River, as well as New Mexico and California. Diplomat James Gadson purchased additional Mexican territory for $10 million in 1853, establishing the present day boundary.

In 1867, William Seward purchased Alaska for $7.2 million from Russia, which had been ready to abandon its designs for an empire so far away. The same year, Canada gained its independence from Britain.

The Spanish American War of 1898 proved Hawaii to be of strategic importance to the US Navy and it was annexed from Spain as well as Puerto Rico.

By 1912, all of the territories of the lower 48 were admitted as states. Alaska and Hawaii joined the Union in 1959, completing the current formation of the United States.