Pre-Capitalist Economic Formations by Karl Marx http://hiaw.org/defcon6/works/1857/precapitalist/ch01.html
True Socialism by Karl Marx and Frederick Engels https://marxistleninists.org/M&E/1845/german-ideology/ch04b.htm
Lenin: 1905/3rdcong2: SPEECHES IN THE DEBATE ON THE ADDITIONAL RESOLUTION TO THE PARTY RULES ON PERIODIC CONFERENCES OF REPRESENTATIVES OF VARIOUS PARTY ORGANISATIONS https://www.marxists.org/archive/lenin/works/1905/3rdcong2/26.htm