". internecine war; the red republicans on the one hand, and the black imperialists on the other." on the basis of those clues, a definition for the word internecine might be republicans opposing forces imperialists

Opposing forces.

Explanation:

" . . internecine war; the red republicans on the one hand, and the black imperialists on the other."

The above excerpt shows a comparison of two things, that are pitted against each other. the red republicans on the one side and the black imperialists on the other side. The only meaningful word that is suggestive of the word "internecine" is "opposing forces". Then, the whole idea is the war of the two opposing forces of the red republicans and the black imperialists.