An ethnic group is a group of people that belong to the same natoinalistic or sometimes racial/cultural background.
africans latinos
china
Hispanic
asian alone
The Jewish, the gypsies, and the disabled
genicide is mass murder of a people of specific religion, ethinic group, or race
the hausa are the largest ethinic group in nigeria almost all hausa are muslims
Chinese and African Americans
sev
I am assuming you mean the United States. The third largest ethnic group in the US is African-American. Although technically not a single ethnic group, African-American is defined as one in the American census. It is preceded by German and Irish.
It is untrue to say that "everyone is a different ethnicity." By definition, an ethinic group is a set of many more than one person who share cultural values, so for each ethnic group there are many people who have that same ethnicity.
An ethnic group is a community or population that shares a common cultural background, heritage, language, or ancestry. Members of an ethnic group often identify with one another based on these shared characteristics and may have a distinct sense of belonging or identity.