How did Cartesian dualism create the mind-body problem?

Cartesian dualism created the mind-body problem by defining mind and body as two fundamentally distinct and complete substances, which made their interaction difficult to explain.12

René Descartes characterized matter as an extended substance that occupies space and follows mechanical laws, while defining mind as an immaterial, nonextended substance whose essence is consciousness or thought. By separating these into two radically different orders of being, Descartes faced the challenge of explaining how an immaterial mind could causally influence a physical body, and vice versa.2314

Descartes proposed interactionism, suggesting this causal link occurred in the pineal gland, but he could not provide a satisfactory account of how such interaction is possible between two such alien substances. This difficulty led to the mind-body problem—the ongoing philosophical struggle to explain how mental phenomena, such as consciousness and intentionality, relate to physical phenomena. Subsequent thinkers attempted to resolve this by proposing alternatives like occasionalism or parallelism, while others eventually rejected dualism in favor of monistic theories.145