The development of the population policies in the 20th century were due too multiple factors, the most important of which were:
- Fertility rates were starting to lower down, especially in the ''western world'' in the second half of the 20th century. - Increased demand for labor force. - The World Wars, especially the second one caused huge migration movements. - Millions of people from less developed countries were trying to migrate to more developed countries in search of a better life.