Lenin: 123. TO THE CENTRAL COMMITTEE OF THE R.S.D.L.P. https://www.marxists.org/archive/lenin/works/1905/sep/30cc.htm
Opportunism, and the Collapse of the Second International http://www.marx2mao.com/Lenin/OCSI15a.html
The German Ideology by Marx and Engels: Saint Max https://marxistleninists.org/M&E/1845/german-ideology/ch03c.htm
The German Ideology by Marx and Engels: Saint Max https://marxistleninists.org/M&E/1845/german-ideology/ch03b.htm
Revelations of the Diplomatic History of the 18th Century by Karl Marx http://hiaw.org/defcon6/works/1857/russia/ch05.html