While I am most certainly American, "American" isn't an ethnicity in the way "English" is. Americanism is about political citizenship, not ancestry.
an ethnic group, though we tend to prefix it with "Native." The problem is that we in the United States of America also use the word "American" to mean "a citizen of the United States of America," which tends to confuse the issue.
People all around the world do that, too. (That is, if you substitute "American" with the equivalents in various languages.) Nobody, to my knowledge, uses "American" without the prefix "Native" to refer to any ethnicity.