At the very beginning of the 20th century there was the 2nd Internationale theoretically led by Karl Kautsky, the official heir to Friedrich Engels who died in 1895. He spoke about a moderate kind of evolutionary (instead of revolutionary) Marxism which went out of fashion during WWI. read more
Popper believed that Marxism had been initially scientific, in that Marx had postulated a genuinely predictive theory. When these predictions were not in fact borne out, Popper argues that the theory avoided falsification by the addition of ad hoc hypotheses that made it compatible with the facts. read more
Marxism: Marxism, a body of doctrine developed by Karl Marx in the mid-19th century that underpinned almost every socialist movement of the 20th century. read more