He considers how contemporary police institutions have developed. Police forces worldwide tend to be public rather than private, to concentrate on crime fighting rather than services, and to be professionally trained and recruited. There is, however, great variation in the structure of police forces, which are generally either centralized or, as in the United States, decentralized.
The behavior of the police toward their constituents also varies by nation. As urbanization and industrialization increase, the public finds itself in greater contact with police and may begin to rely on them more for protection. There are also marked differences cross-nationally in the way police relate to political and community life.