Shifts of labels concerning "black" poetry

I was recently running tests on "poetry" on Google's Ngram Viewer. I was curious about the shift of the terms to describe poetry by African Americans. In particular, I wondered about the phrases "Negro poetry," "African American poetry," and "Black poetry."

Graph from Ngram Viewer

Notice that after the 1920s, "Negro poetry" begins to gain considerable mentions in books. The phrase "Negro poetry" declines rapidly during the 1970s replaced by the rapid rise of "Black poetry." You get the sense that poetry by African Americans had its heyday, at least in terms of mentions in books, during the 1970s.

It's not until the mid-1990s that the phrase "African American poetry" begins to gain traction. That increase, of course, is nowhere near the rise that "Black poetry" had. Still, it's been a steady rise.

Related:
• LeRoi Jones vs. Amiri Baraka vs. Black poetry