18 Game of Thrones Season 7 Theories to Read Until the Show Returns

When Bran is touched by the Night's King during one of his visions, it allows the White Walkers and their horde of undead wights to trespass on ground that was formerly magically protected. Now, as he plans to head south of the Wall, it's likely that he'll ruin the protective enchantments that were built into the massive structure, allowing the Night King's armies to breach the Wall.