At independence, the United States consisted of thirteen states covering roughly 2.3 million km². Victory in the Revolutionary War secured lands east of the Mississippi via the Treaty of Paris (1783), while the Louisiana Purchase (1803) doubled the nation's territory, laying the foundation for continental expansion.

Through westward expansion, war, and settlement, the United States reached the Pacific, forming a coast-to-coast nation of ~8.5–9.3 million km². Key events included the annexation of Texas, the Mexican–American War, and the California Gold Rush.

While territorial expansion slowed, the U.S. emerged as a global power, reaching ~9.37 million km² with Alaska (1867) and Hawaii (1898). Overseas territories like the Philippines, Puerto Rico, and Guam marked its transition from continental to international influence.