The United States of America is one of the world's largest countries based on both population (over 300 million) and area. It is made up of 50 individual states and Washington, D.C., its national capital. Each of these states also has their own capital city and other very large and small cities.These state capitals however vary in size but all are important to politics in the states. Interestingly though, some of the largest and most important cities in the U.S.