Why are some Americans named to indicate their ancestry? It is not common to say, German Americans, or Russian Americans; however, African American, and Asian American are accepted nomenclatures. Even President Obama's Wikipedia entry reads, "He is the first African American to hold the office."
What is the origin / reason for this?
Update: "I am an American. Black. Conservative. I don't use African-American, because I'm American, I'm black and I'm conservative. I don't like people trying to label me. African- American is socially acceptable for some people, but I am not some people." -Herman Cain