Final answer:
The biggest legacy left by Marx is his writings on economic theory and class struggle.
Step-by-step explanation:
The biggest legacy left by Marx is his writings on economic theory and class struggle. Marx and his collaborator, Friedrich Engels, used a scientific analytical process to show that throughout history, resolving class struggles caused changes in economies. They believed that a socialist society would be created after workers rebelled against capitalistic owners and seized the means of production. These ideas form the basis of the sociological perspective of social conflict theory.