The states of Texas, Louisiana, Mississippi, Alabama, and Florida all touch the Gulf of Mexico and are collectively known as the Gulf States. The influence of the Gulf of Mexico on the history of these states has been profound, and extends to the rest of the nation as well.
The Spanish showed an early interest inf the Gulf of Mexico when they settled Havana in 1519, from which they launched the expedition of Cortes that invaded the Mexican interior from Vera Cruz. The Spanish settled Pensacola in 1697 and the French settled Mobile in 1702 and New Orleans in 1718.
The Gulf was increasingly important due to the role of the Mississippi River as the natural outlet for products from the region west of the Alleghenys. The United States secured this outlet through the Louisiana Purchase of 1803.
In 1819, in order to secure for America the Gulf outlets of the rivers in its southern interior, the Adams-Onis Treaty obtained the cession of all the Floridas from Spain. At this point, America had control of the Gulf coast as far west as the Sabine River between Louisiana and Texas, and the annexation of Texas and the Mexican War confirmed its control as far as the Rio Grande.
Having established its control over the mouth of the Mississippi, the next concern for the United States was the island of Cuba, standing at the entrance to the Gulf waters. Prior to the Civil War, some southerners advocated the annexation of Cuba, as shown by the Ostend Manifesto.
In the end, Spain was ousted from its last possessions in the New World by the Spanish-American War in 1898. While Cuba did not come directly into U.S. possession, the Platt Amendment guaranteed a great deal of American influence until it was terminated in 1937 in the period of the Good Neighbor policy.
In geographical terms, a "gulf" is ordinarily smaller than a "sea," but the Gulf of Mexico, at 700,000 square miles, is substantially larger than some recognized seas, such as the Baltic Sea, which has about 163,000 square miles including three gulfs.