My original comment is meant to refer to the concept of Materialism, which contains the concepts of Marxist Dialectical and Historical Materialism. Materialism is a "reality-focused" branch of philosophy and analysis, contrasted with Idealism, which is idea-focused.

The connection to liberalism and fascism is because Liberalism is Idealist as opposed to Materialist. The Liberal answer to "where does fascism come from?" Would be "demagogues like Trump rising to power, racism, xenophobia, etc," yet when you ask why those ideas are present or not present, the Liberal cannot answer genuinely.

For Marxists, fascism is a consequence of Capitalism's decline, resulting in the Petty Bourgeois elements of society, ie the "Middle Class," sliding into worse conditions and allying with the Bourgeoisie against the Proletariat. In the Weimar Republic, Capitalism was declining and genuine Communism was gaining steam, with the KPD at the forefront and the SPD representing the moderate Socialists, so fascism gained power as a reaction. Communism and Socialism gained appeal among the Lower Classes while fascism gained power among the Liberals, ie the Middle and Upper Classes.

The other works listed by other commenters are great, but my personal favorite work on the subject is Elementary Principles of Philosophy.