The United States of America is a federal republic and comprises of one federal district and 50 states. Totally, United States is spread around 9.83 million km2 and is the third largest nation in terms of total area. It has a population of about 318 million individuals and is the third largest country in terms of population. USA is also one of the worlds most multicultural and ethnically diverse nations. This is because of large amount of immigration from other nations. The climate and geography of United States is also highly diverse, hence it houses a wide array of wildlife.