Final answer:
Marx believed that capitalism would collapse due to extreme inequalities, leading to a revolution and the establishment of communism. However, he did not provide adequate detail on the material conditions necessary for the revolution to occur. Marx also underestimated the challenges of creating a wealthy and classless society.
Step-by-step explanation:
Marx predicted that inequalities of capitalism would become so extreme that workers would eventually revolt. This would lead to the collapse of capitalism, which would be replaced by communism. Marx believed that communism was a more equitable system than capitalism.
To boil it down to a very simple level, Marx never described in adequate detail when the material conditions for a socialist revolution were possible. Across the vast breadth of his books and correspondence, Marx (and his collaborator Friedrich Engels) argued that each nation would have to reach a critical threshold in which industrialism was mature, the proletariat was large and self-aware, and the bourgeoisie was using increasingly harsh political tactics to try to keep the proletariat in check. There would have to be, and according to Marxism there always would be, a major economic crisis caused by overproduction.
Marx had underestimated the difficulties of creating a society that was both wealthy and classless. One of the central contradictions of Communism was that it required at least a temporary centralization of government power. The disinclination of the authoritarian governments of Eastern Europe to relinquish these powers led many to fear that the anti-Communist revolutions of the late 1980s would lead to bloody counterrevolutions and civil wars. Instead, most Communist leaders decided the wisest course of action was to permit free elections.