Adams–Onís Treaty
Many territories that had been part of New Spain became part of the United States after 1776 through various wars and treaties, including the Louisiana Purchase (1803), the Adams–Onís Treaty (1819), the Mexican–American War (1846–1848), and the Spanish–American War (1898). There were also several Spanish expeditions to the Pacific Northwest, but Spain gave the United States all claims to the Pacific Northwest in the Adams–Onís Treaty. There were several thousand families in New Mexico and California who became American citizens in 1848, plus small numbers in the other colonies.