What did Manifest Destiny have to do with the expansion of the United States?
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The doctrine of Manifest Destiny emerged in the United States in the early 1800s and by the 1840s had taken firm hold. Adherents believed that Americans had a God-given right and duty to expand their territory and influence throughout North America. Manifest Destiny was a rallying cry for expansionism and prompted rapid U.S. acquisition of territory during the 1800s. The acquisitions began in 1803 with the purchase of Louisiana Territory from France; in 1819 Florida and the southern strip of Alabama and Mississippi (collectively called the Old Southwest) were acquired from Spain in the Adams-Onís Treaty; in 1845 Texas was annexed after white settlers fought for and declared freedom from Mexico, forming the Republic of Texas and petitioning the Union for statehood; in 1846 the western border between Canada and the United States was determined to lie at 49 degrees north latitude, the northern boundary of what is today Washington State; in 1848 by the Treaty of Guadalupe Hidalgo, the United States secured New Mexico and California after winning the Mexican War (1846–48); and in 1853 southern Arizona was acquired from Mexico in the Gadsden Purchase. With the 1853 agreement the United States had completed the acquisition of territory that makes up the contiguous states.
The expansionist doctrine of Manifest Destiny was again invoked as justification for the Spanish-American War (1898), which was fought over the issue of freeing Cuba from Spain. Spain lost the war, dissolving its empire. Cuba achieved independence (though it was occupied by U.S. troops for three years). By the close of the nineteenth century, Manifest Destiny had resulted in U.S. acquisition of the outlying territories of Alaska, Hawaiian Islands, Midway Islands, the Philippines, Puerto Rico, Guam, Wake Island, American Samoa, Panama Canal Zone, and U.S. Virgin Islands.