Why is America a multicultural, multiracial and multireligious society?

To talk about American culture, we must talk about American history, which is very short, just two or three hundred years. In this short period of two or three hundred years, the national structure of the United States has been constantly changing. At first, Spain, the Netherlands, Portugal and other nationalities immigrated to the British Isles in the early days, and many indigenous Indians, Chinese and African-American slaves became free men. Along with other immigrants, they moved from South America to North America, from east to west. It can be said that America is a hodgepodge of nationalities. So many immigrants from a country have brought various cultures, customs, religions, etc. This makes American immigrant society present a multi-level social outlook. Among them, the mainstream is the white culture with Christian background brought from European countries such as Britain. Other ethnic minorities are not dominant among them.