Vacancy is the collection of a gap, and it is the abode of fear from the flocks of countries or their outskirts, and it may be between mountains or on the coasts of water.
And the Islamic outposts are those places that were opened by the Muslims and inhabited by the Mujahideen, to set off where the next place to open it or to perform the mission of calling to God in it or in its vicinity from places and install the foundations of Islam there.
The Muslims left the Arabian Peninsula after all of them were condemned to Islam, they went out to its north, east and west, sweeping away the king of the Crusaders and tearing apart the king of the Romans, for God provided the conquerors with tremendous spiritual faith cards that enabled them to spread the light of God Almighty to the corners of the world