民主主义 — 'democracy as an -ism' — is the suffix-heavy form preferred in 20th-century political theory writing. Mao Zedong's 1940 essay 《
新民主主义论》 ('On New Democracy') used
新民主主义 to label the bourgeois-democratic stage of the Chinese revolution led by the Communist Party — a foundational text of CCP ideology. In casual modern speech,
民主 alone usually suffices for 'democracy';
民主主义 sounds textbook-formal.