Migration or war. Why a person would want to leave their place for a specific reason is a push factor and a pull factor is why a person wants to move to a specific place.
Push factors are the reasons for leaving a country e.g drought, wars, no work available. Pull factors are the reasons that attract a person to the new country e.g freedom from persecution, more jobs...
Push factors is when something makes you move out of your country such as the lack of jobs, wars, lack of food, and drought. A pull factor is when something you like is somewhere like good jobs, big...