The United States lacks the historical places and cultural antiquities that Europe is proud of. So Americans located their national identity in wonders of nature. North America has plenty of unique scenic landscapes to see and just a few cities worth to visit. In the USA big is always beautiful, Grand Canyon, Niagara Falls, Mammoth Cave to name just a few.
Beginning in 1857, the United States began annexing small islands in the Caribbean and Pacific. By the end of the century, it had claimed almost a hundred of them. At the time, these islands had no indigenous populations and no strategic value, but they had "white gold." The reason was guano, the excrement of seabirds, which is a highly effective fertilizer. The next phase of U.S. colonial expansion was the Spanish-American War of 1898. It led to the acquisition of Puerto Rico, Guam, and the Philippines by the United States, and dominance in Cuba. The US also purchased Alaska from the Russian Empire and three Virgin Islands from Denmark. Some overseas possessions were lost, but today the United States of America consists of not only 50 states and the federal District of Columbia, but also of overseas territories in the Pacific and the Caribbean.
