During the 19th century, Karl Marx and Friedrich Engels extended the concept of materialism to elaborate a materialist conception of history centered on the roughly empirical world of human activity (practice, including labor) and the institutions created, reproduced, or destroyed by that activity (see materialist conception of history). Later Marxists developed the notion of dialectical materialism which characterized later Marxist philosophy and method.
Which era of Marxists rejected the notion of dialectical materialism?  (If the question is unanswerable, say "unanswerable")
unanswerable