Marx (and Engels) found in the American anthropologist Lewis Henry Morgan's work a confirmation of and expansion upon his own materialist approach. Similarities he found included Morgan's division of mankind's early development into distinct stages, each the necessary forerunner of its successor; a theory of historical development; the importance of "productive forces"; and an awareness of the social contradictions of private property. Marx knew Morgan did not share his political sympathies, but he and Engels did not see or ignored evidence that Morgan was not an historical materialist. Marx and Engels through their enthusiasm for Morgan brought their materialist conception of history into contact with the important question of the nature of kinship bonds, even if they did not resolve it themselves.