African Americans (also referred to as Black Americans or Afro-Americans) are an ethnic group of Americans with total or partial ancestry from any of the black racial groups of Africa.  The term may also be used to include only those individuals who are descended from enslaved Africans.  As a compound adjective the term is usually hyphenated as African-American. 
Black and African Americans constitute the third largest racial and ethnic group in the United States (after White Americans and Hispanic and Latino Americans). Most African Americans are descendants of enslaved peoples within the boundaries of the present United States.  On average, African Americans are of West/Central African and European descent, and some also have Native American ancestry. According to US Census Bureau data, African immigrants generally do not self-identify as African American. The overwhelming majority of African immigrants identify instead with their own respective ethnicities (~95%). Immigrants from some Caribbean, Central American and South American nations and their descendants may or may not also self-identify with the term.
African-American history starts in the 16th century, with peoples from West Africa forcibly taken as slaves to Spanish America, and in the 17th century with West African slaves taken to English colonies in North America. After the founding of the United States, black people continued to be enslaved, with four million denied freedom from bondage prior to the Civil War. Due largely to notions of white supremacy, they were treated as second-class citizens. The Naturalization Act of 1790 limited U.S. citizenship to whites only, and only white men of property could vote.  These circumstances were