Césaire was a member of the Communist Party of Martinique. He developed ideas that expanded Marx's ideology of proletariat versus the ruling powers, socialism versus capitalism. Discourse on Colonialism is often addressed by critics in terms of whether it either conforms to or breaks with Marxist orthodoxy. However Césaire emphasizes ideas that contribute to thinking about colonialism, fascism and revolution. Césaire did build upon Marxist thought and he expanded it. He recast Western Civilization's history in order to examine the interconnectedness of colonialism and fascism and to demonstrate that these threaten humanism on which Western Civilization is founded. His revisions of Marxism followed in line with his predecessors W.E.B. DuBois and M.N. Roy and suggest that the proletarian revolution takes second place to the anticolonial struggle. His conclusion is the vision of a total overthrow of racism and colonialism, in any guise.
[For more information, see "A Poetics of Anticolonialism" by Robin D.G. Kelley from which this answer is drawn.]