Global trigger factors for urbanization include economic, demographic, social, technological, cultural, political, and environmental changes. These triggers lead to processes of urban change such as suburbanization, urbanization, counterurbanization, and peripheral urbanization. Urbanization occurs when cities grow at the expense of the countryside. Suburbanization is when the inner ring or commuter belt grows relative to the urban core. Counterurbanization is when population loss in the urban core exceeds gains in surrounding areas.