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Spain establishes its first permanent settlement in the Americas, St. Augustine in Florida.
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After the Seven Years' War (French and Indian War in North America), Spain cedes Florida to Great Britain in the Treaty of Paris.
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With the Treaty of Paris ending the American Revolutionary War, Great Britain recognizes the independence of the United States of America, but the territorial boundaries are not precisely defined.
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Spain reclaims Florida from Great Britain through the Treaty of San Lorenzo (also known as Pinckney's Treaty), effectively ending British rule in Florida.
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The Spanish American Wars of Independence begin, with revolts against Spanish rule in various colonies, including those in the present-day United States.
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The Adams-Onís Treaty (also known as the Transcontinental Treaty) is signed between the United States and Spain, defining the border between the two countries along the 42nd parallel from the Gulf of Mexico to the Rocky Mountains. Spain cedes Florida to the United States.
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Mexico achieves independence from Spain, inheriting territorial claims in the Southwest United States, including Texas and California.
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President Andrew Jackson sends a diplomatic note to Spain demanding the right to deposit the US debt to Spain in the Florida territory, effectively asserting US sovereignty over Florida.
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The Texas Revolution erupts as Texans seek independence from Mexico.
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The United States annexes Texas, which had declared independence from Mexico in 1836 and was recognized by the US in 1837.
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The Mexican-American War is fought between the United States and Mexico, resulting in the United States gaining vast territory, including California, New Mexico, Arizona, Nevada, Utah, and parts of Colorado and Wyoming.
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The Treaty of Guadalupe Hidalgo is signed, officially ending the Mexican-American War and recognizing the United States' annexation of the territory gained during the war.
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The Gadsden Purchase is made, in which the United States purchases a strip of land from Mexico along the southern border of Arizona and New Mexico, including parts of what is now southern Arizona and southwestern New Mexico.