It could be said that the theme, or central idea, of "The Negro Speaks of Rivers" is the long history of the black race. What evidence from the poem supports this view?

The main idea of "The Negro Speaks of Rivers" is the long history of the black race. This theme can be identified when the speaker in the poem mentions that he has a connection or something that links him to some great rivers. He's trying to explain that, like the rivers that have seen many civilizations grow and flourish, he has also grown and flourish with the rivers.

The speaker mentions four rivers:

- The Euphrates

- The Congo

- The Nile

- The Mississippi

All of these rivers reference different civilizations, and the speaker tries to link the last river he mentions - the Mississippi - to the history of slavery.

So, we can definitely see how the history of the black race is the main idea in this poem, written to explain that, like rivers, the black race has existed as long as history goes, and it has seen civilizations thrive and expand just like rivers.