He used to be a member of the Chinese gang.

He experienced the harsh reality of the underbelly of society.

In psychology, it is important to understand the mechanism behind human behavior.

We adopted the AA system to start a new project.

Monarchy still exists in some countries.

Bureaucracy plays an important role in the operation of the government.

Manorialism was one of the economic systems in medieval Europe.

This change in zoning will have a significant impact on urban planning.

Polygyny is a social system where one man marries multiple women.

Monogamy is a system where one man marries only one woman.