U.S. Precedents to Consider when Thinking About Crimea.

The United States purchased the Louisiana territory from France in 1803. It purchased the Florida territory from Spain in 1819. It made the Gadsden Purchase from Mexico in 1853-54. It purchased Alaska from Russia in 1867. It purchased the U.S. Virgin Islands from Denmark in 1917.

Territories were acquired from Great Britain in 1818 and 1842 by treaties.

Texas and Hawaii were acquired by the United States after their residents had overthrown existing governments, established new states, and then applied for admission to the Union.

The United States acquired much of the southwest, Puerto Rico, and Guam by conquest (in the war with Mexico in the 1840s and the Spanish-American War of 1898). It also obtained sovereignty over the Philippines and protectorate status over Cuba in the Spanish American War.

Note that the administration of Puerto Rico has changed over the long period in which it has been U.S. territory.

According to Wikipedia:

An American Indian reservation is an area of land managed by a Native American tribe under the United States Department of the Interior's Bureau of Indian Affairs. There are about 310 Indian reservations in the United States, meaning not all of the country's 550-plus recognized tribes have a reservation—some tribes have more than one reservation, some share reservations, while others have none.

Also according to Wikipedia: The

United States Naval Station Guantanamo Bay............is located on 45 square miles (120 km2) of land and water at Guantánamo Bay, Cuba, which the United States leased for use as a coaling and naval station in the Cuban–American Treaty of 1903. The base is on the shore of Guantánamo Bay at the southeastern end of Cuba. It is the oldest overseas U.S. Naval Base, and the only U.S. military installation in a country with whom the United States has no diplomatic relations. Since 1959 the Cuban government has consistently protested against the US presence on Cuban soil and called it illegal under modern international law.

 According to UNESCO:

In 1932 Waterton Lakes National Park (Alberta, Canada) was combined with the Glacier National Park (Montana, United States) to form the world's first International Peace Park. 

Both parks were designated by UNESCO as Biosphere Reserves in the global network of reserves in 1976, and in 1995 as World Heritage sites. The two parks are administered separately; Glacier National Park is administered by the federal National Park Service under federal legislation.