Aside from Marx, Friedrich Engels also focused on the AMP. In their later work, both Marx and Engels dropped the idea of a distinct Asiatic mode of production, and mainly kept four basic forms: tribal, ancient, feudal, and capitalist. In the 1920s, Soviet authors strongly debated about the use of the term. Some completely rejected it. Others, Soviet experts on China referred to as "Aziatchiki", suggested that Chinese land ownership structures had once resembled the AMP, but they were accused of Trotskyism and discussion of AMP was effectively banned in the USSR from 1931 until the Khrushchev period.