Until recently, south korea had laws in place banning marriage between people who belonged to the same clan. this means that they practiced:

This means that they practiced exogamy. Exogamy is an arrangement where marriage is permitted outside a social group. It is viewed as a combination of two aspects namely biological and cultural. In biological exogamy, it is the marriage of two nonblood-related beings. Whereas in exogamy, it is the marriage outside a particular cultural group.