The Adams–Onís Treaty of 1819, also known as the Transcontinental Treaty or the Purchase of Florida, was a treaty between the United States and Spain in 1819 that gave Florida to the U.S. and set out a boundary between the U.S. and New Spain (now Mexico). It settled a standing border dispute between the two countries and was considered a triumph of American diplomacy. It came in the midst of increasing tensions between the U.S. and Spain regarding territorial rights at a time of weakened Spanish power. In addition to ceding Florida to the United States, the treaty settled a boundary dispute along the Sabine River in Texas and firmly established the boundary of U.S. territory and claims through the Rocky Mountains and west to the Pacific Ocean, in exchange for the U.S. paying residents' claims against the Spanish government up to a total of $5,000,000 and relinquishing its own claims on parts of Texas west of the Sabine River and other Spanish areas under the terms of the Louisiana Purchase.

Onís is a municipality and a parish in the Autonomous Community of the Principality of Asturias, Spain. The municipality is bordered on the north by Llanes, on the south by the province of León, to the east by Cabrales and to the west by Cangas de Onís.

The area of the municipality is 75 km², being more of a third of its territory in the Picos de Europa National Park. The population is dispersed over various population centers, being its capital de Benia de Onís. In 2007, the population is of 920 inhabitants, increasing remarkably during holiday times.

The source of the Güeña River, main affluent of the Sella River, is lowest point of the municipality with 175 m. Part of the Picos de Europa, the Pico de Verdilluenga is the highest point of the municipality with 2,129 m.