Cultural diffusion is the spread of ideas between cultures through movement of people, goods, or ideas. There are different types of diffusion including expansion, contagious, hierarchical, and relocation diffusion. Population growth is influenced by birth and death rates and follows a demographic transition from high birth/death rates to low birth/death rates as development increases. Rostow's model of development proposes countries progress through five stages from traditional to modernized societies, while dependency theory argues poorer countries remain limited by relationships with wealthier countries.