which community do the latter belong to to?
An ethnic group of Americans.
African Americans
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. 
which nationality of the slave community is discussed here? Slavery in the United States. to what is this title given? A book. who is the author? John W. Blassingame who are considered slaves in the country referred? Legal institution of human chattel enslavement, primarily of Africans and African Americans.
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African Americans [SEP] Introduction
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 "African American" generally denotes descendants of enslaved black people who are from the United States, while some recent black immigrants or their children may also come to identify as African-American or may identify differently. African Americans constitute the third largest ethnic group and the second largest racial group in the US, after White Americans and Hispanic and Latino Americans. Most African Americans are descendants of enslaved peoples within the boundaries of the present United States.