An angry snarl of resentment and righteous anger, an indictment of centuries of crimes. It hides under the rather innocuous title 'Discourse of Colonialism', but instead might be appropriate 'Damn you and damn your hypocrisy and hate that led to hundreds of years of atrocities', or something like that.
The book moves from condemnation of wars and injustice, to attacks on now-obscure colonial theorists and 'racialists'. Cesaire makes the bold statement that Nazism is so infamous in Europe because it committed the same atrocities that the Europeans did to other, non-white nations. Slavery, mass extermination, economic exploitation, racial/social engineering, and so forth.
Cesaire does stray into a few grey areas, though. He cites the Soviet Union as a possible source of post-colonial liberation. That state is just imperialism with a new coat of paint. He also does make a few wrong statements which modern anthropology has corrected, but he'd likely be fine with that. In fact, he'd be proud to see the advances in some of these fields.
These little nitpicks do not detract from the overall strength of his feeling. The book itself is not without flaws, but it helped to spark a movement, of peoples rising up and a radical change in intellectual discourse. That alone gives it a place in history.