Complex sentence: Rural depopulation is a phenomenon affecting rural locales in both developed and developing countries, whereby net population movement leaves rural places with decreasing population and urban places with increasing population, caused by the the migration of people from rural areas to urban areas.
Split into simpler sentences: Rural depopulation is a phenomenon affecting rural locales in both developed and developing countries, whereby net population movement leaves rural places with decreasing population and urban places with increasing population. It is the migration of people from rural areas to urban areas.