3. THE WHITE WALKERS’ MARCH
We’ve watched as the White Walkers amassed an army of the undead to eventually take the south. They remained an elusive menace in the icy lands beyond the wall until the very end of season two when they decimated the Night’s Watch at the Fist of the First Men in a battle we never got to see. Their next major attack was at Hardhome, which resulted in thousands more added to the Night King’s army of wights.
Then the Night King, using Bran, broke through the mystical barrier guarding the three-eyed raven and killed him. We know that they’re generally heading south and we know that the White Walkers and the undead can’t just breach the Wall, since its protected by magical safeguards, as Benjen explain in the episode, “Winds of Winter” (written by Benioff and Weiss). It’ll be interesting to see how they intend to get through it in season 7.