The United States covers an area of over 9.62 million square kilometers, second only to Russia and Canada [2][3]. Its population also exceeds 300 million, less than that of China and India. The United States is the most multicultural country in the world, including almost all immigrants from all over the world. At the same time, America is also the most developed country in the world. In 2008, its GDP was as high as 14.3 trillion US dollars, accounting for 23% of the global GDP (2 1% in terms of purchasing power parity).

The United States originated from 13 British North American colony which broke away from British rule. 1776 On July 4th, the colonial representatives of 13 jointly issued the Declaration of Independence. After an arduous war of independence, the Treaty of Paris was signed with Britain in 1783, and it has been recognized by all countries in the world since then.