The development of Britain and the United States is closely related. This paper summarizes the ethnic relations between Britain and the United States in different periods, and tells its main characteristics and reasons. Colonial period: subordination at the beginning of independence: hostility after the civil war: the relationship between the two countries gradually improved to World War I: alliance. When the United States was just founded (A.D. 1776), the two countries were hostile, because the United States was a British colony before the founding of the People's Republic, and then it was irrelevant for a long time (the United States was busy with civil war and racial discrimination), and then there was competition. The United States tried its best to catch up with Britain until it successfully surpassed it in the early 20th century. But at this time, the United States owed a lot of foreign debts to Britain because of its development. After the outbreak of World War I, Britain, France and Russia took control of maritime hegemony. The United States took the opportunity to form an alliance with Britain, sold a lot of arms to its allies, and forced Britain to cancel its foreign debt at the expense of sending troops, leaving Britain with a large amount of foreign debt. During World War II, the two countries did not really come together until today, and Britain became America's best ally.