All societies undergo adjustments in their social structure and culture over time. This may result from contact between societies or from alterations in the physical environment such as prolonged drought. Further, changes in development practice and in international aid influence national goals and priorities with respect to different sectors and regions. How change is brought about and what it is that changes are important issues that need to be addressed.
The profound impact of forces for change on diverse societies finds expression in patterns of apparently increasing uniformity between countries and cultures. In demographic terms, these include rapid rates of national population growth, and internal migration of people from rural to urban areas coupled with urban expansion.