Saint Thomas: "The reason for this was that if foreigners were allowed to meddle with the affairs of a nation as soon as they settled down in its midst, many dangers might occur, since the foreigners not yet having the common good firmly at heart might attempt something hurtful to the people."
Father Joseph Ratzinger wrote a Vatican paper under JPII that says something about taking into consideration, when accepting “refugees”, the disruptions and burdens imposed upon the “welcoming” populace.