When Jon Snow met Daenerys Targaryen on Game of Thrones, it didn't go exactly as fans might have hoped. While Dany insisted this "King in the North" bend the knee, Jon talked in terms of apocalyptic end times, citing the oncoming "Long Night." He isn't the only one talking about it either. We've heard several characters worry about this phenomenon over the last few episodes. But what is the Long Night on Game Of Thrones and why does it worry them so?
For those of you who haven't listened to Shireen or checked out "Westeros: A History" (also known as The World of Ice and Fire), here's a little history on the usage of the phrase: Up until about 298 AC (when our story begins), the phrase was used to refer to a historical period that happened back around ~8,000 BC, during the era known as "The Age of Heroes." During the records of that period of history, a Great Winter came, the type that Planetos only sees once every few thousand years.
Said "Great Winter" went on for several decades, though the exact length isn't recorded. In the middle of it, a secondary phenomenon occurred, which compounded the effects, in which "a terrible darkness" fell across the world, which lasted "a generation." (We estimate that to be ~10 years, give or take.)
As fans can imagine, the already difficult "Great Winter" for humans to live through was only made worse by this engulfment into darkness. There was a massive famine that spread across the continent. But even worse, during this darkness, a race of "demons" (which we know to be White Walkers and wights) first came down from the far northern reaches of Westeros and attempted to conquer.
The Children, who we now know to have been responsible for these creatures, and the First Men banded together to take down the invasion. Said battles are what spawned the legend of Azor Ahai, with his flaming sword that defeated the White Walkers.
And while Maester Ebose said he believes in the Long Night because there are too many legends that reference it, we have proof that something terrible did occur in this period: the Wall. The Wall was built post-"Great Winter," with the help of The Children and Giants, both of whom chose to live north of it ever after to keep these creatures from ever attacking Westeros again.
So why does everyone in Westeros think that the Long Night is coming back again? In our story, it starts with Melisandre, who has this vision from R'hllor that the next coming of winter will bring a Long Night with it. This is what drives her to find Azor Ahai (The Prince Who Was Promised) reborn. That's what brings her to Westeros in the first place, blundering about from Stannis to Jon Snow to Dany, trying to interpret the signs she sees in the flames as to who will save the world.
But she's not the only one. The Night's Watch is concerned up at the Wall at the sudden increase in White Walker activity, as Lord Mormont told Tyrion back in Season 1. Above the Wall, Mance Rayder sees the same signs and gathers all of the "free folk" (who are really just the descendants of those who were unlucky enough to live on the wrong side when the Wall went up). His aim: to get his followers to the right side of the Wall in order to survive what is starting to look like an invasion.
Those south of the Wall who are bothering to pay attention are concerned about the length of the coming winter. The summer, which is drawing to its end as we begin our story, is one that lasted an abnormally long time. Extremely long summers -- this one has lasted since before Robert's Rebellion began -- are usually followed by very long winters. But the Long Night isn't on their radar -- until Jon Snow sees the forces of the Dead at Hardhome.
As everyone will recall, when the Army of the Dead arrives on screen, they don't just walk on up and rattle some sabers. As we were reminded in the premiere, a darkened squall of snow bringing whiteout conditions precedes their entrance. We saw this at Hardhome, too. It's a good bet that when we run into the Army again, their snow-squall calling card will precede them.
These whiteout conditions block out the sun. As more and more die, and the Army increases, this snow-squall will become larger and larger, surrounding the invading forces. At this point, it's just a matter of how and when they get over the Wall, not if. And when they do, that darkness comes with them.
Of course Jon Snow is terrified. He's determined to get his dragonglass weaponry back to the Northern Houses while he's still only traveling through winter storms and not that level of darkness. The question is: What will it take to get Dany to believe him and join the cause?