How did migration affect the population of the countries? need ! : '(

Migration is moving to another country to permanently or semi-permanently stay there. It is one of the main causes of population change. The basic principle is when you move from country A to country B, country A loses one citizen and country B gains one. Due to economic and political reasons, the rate of migration is increasing. On one hand, migration can help increase the human resources of countries lacking it. It can help balance population between countries. On another, mass migration can cause economic problems. Currently, Europe is facing major crisis in catering immigrants from Syria and other countries.