"The men who formed the Night's Watch knew that only their courage shielded the realm from the darkness to the north. They knew they must have no divided loyalties to weaken their resolve. So they vowed they would have no wives nor children.
Yet brothers they had, and sisters. Mothers who gave them birth, fathers who gave them names. They came from a hundred quarrelsome kingdoms, and they knew times may change, but men do not. So they pledged as well that the Night's Watch would take no part in the battles of the realms it guarded."
They kept their pledge. When Aegon slew Black Harren and claimed his kingdom, Harren's brother was Lord Commander on the Wall, with ten thousand swords to hand. He did not march. In the days when the Seven Kingdoms were seven kingdoms, not a generation passed that three or four of them were not at war. The Watch took no part. When the Andals crossed the narrow sea and swept away the kingdoms of the First Men, the sons of the fallen kings held true to their vows and remained at their posts.