The explanation for the recent population decrease is the fall of communism in Albania in the late twentieth century. That period was marked by economic mass emigration from Albania to Greece, Italy and the United States. Four decades of total isolation from the world, combined with its disastrous economic, social and political situation, had caused this exodus. The external migration was prohibited outright during the communist era, while internal migration was quite limited, hence this was a new phenomenon. At least 900,000 people left Albania during this period, with about 600,000 of them settling in Greece. The migration affected the country's internal population distribution. It decreased particularly in the north and south, while it increased in the center within the cities of Tirana and Durrës.