In the United States, tourism is a large industry that serves millions of international and domestic tourists yearly. Foreigners visit the U.S. to see natural wonders, cities, historic landmarks, and entertainment venues. Americans seek similar attractions, as well as recreation and vacation areas. Tourism in the United States grew rapidly in the form of urban tourism during the late nineteenth and early twentieth centuries. By the 1850s, tourism in the United States was well established both as a cultural activity and as an industry. New York City, Los Angeles, Chicago, Boston, Philadelphia, Washington, D.C., and San Francisco, all major U.S. cities, have attracted numerous tourists since the 1890s. By 1915, city touring had marked significant shifts in the way Americans perceived, organized, and moved. During the early 20th century, many more people started to travel, partly because of the spread of the automobile. Similarly air travel revolutionized travel during 1945–1969, contributing greatly to tourism in the United States. Purchases of travel and tourism-related goods and services by international visitors traveling in the United States totaled $10.9 billion during February 2013. In the U.S., tourism is among the three largest employers in 29 states, employing 7.3 million in 2004, to take care of 1.19 billion trips tourists took in the U.S. in 2005.[citation needed] As of 2007, there are 2,462 registered National Historic Landmarks (NHL) recognized by the United States government. As of 2023, New York City is the most visited destination in the United States, followed by Miami, Los Angeles, Orlando, and San Francisco.