The United States of America is a federal republic consisting of 50 states, with population of 318 million people. Tourism is a large industry in this country and it serves millions of international and domestic tourists yearly. Tourism in the United States grew rapidly in the form of urban tourism, during the late 19 century and early 20 century. Tourism is either the first, second or third largest employer. When they are traveling abroad, most popular destination that Americans visit is London. And most popular destination for tourists in the United States is New York City, which is also the most expensive United States city. For tourism in the United States, most important are national parks, city tourism, marine tourism and attractions. The United States has more than 100 national parks. Yellowstone National Park in Wyoming, Montana and Idaho is the first national park in the world and the most visited national park is Great Smoky Mountains National Park in South Carolina. City tourism has an important role in the overall tourism of the United States. The most important state in the United States for marine tourism is Hawaii with its numerous beaches. In the United States there are also many attractions, visited by a great number of tourists every year.