Hardhome
Jon Snow sails north to bring the free folk south of the Wall, and the dead arrive first. What the Watch had treated as a story becomes a massacre on a beach with thousands of witnesses ÔÇö and every single one of them is added to the enemy's army as they watch. The Night's King raises his arms, and the argument about whether the Others are real is over.
The fuller tale
Jon Snow, Lord Commander of the Night's Watch, made the least popular decision in the order's history: that the free folk had to be brought south of the Wall. Not out of mercy ÔÇö though there was that ÔÇö but out of arithmetic. Every wildling left to die north of the Wall was a soldier for the other side.
So the Watch sailed to Hardhome, where thousands were penned on a beach with no food and nowhere to go, and spent a day arguing the case to people whose grandfathers the Watch had killed. Some agreed. Many did not. And while the argument was still going on, the weather changed and the thing on the ridge arrived.
What happened on that beach was not a battle. It was thousands of people trying to get into boats. Dragonglass worked; ordinary steel did not; Valyrian steel worked and there was one blade of it present. At the end of it the Night's King walked down to the waterline in front of the retreating ships and raised his arms, and every single person who had died that day stood up.
The argument that ended
For eight thousand years the question of whether the Others were real had been a matter of opinion. After Hardhome it was a matter of testimony: hundreds of witnesses, half of them free folk who would carry the story south, and a Lord Commander who had seen it from a boat.
It changed nothing at all in the south, where the great houses were entirely occupied with each other and regarded reports from the Wall as the usual northern nonsense. The dead gained an army in an afternoon; the living lost another four years arguing about a chair.
Elsewhere in the wiki
 See the world as it stood in 301 AC What became of it  if an ending is written, it is here. Spoilers.
The chronicle records no ending here ÔÇö or none the maesters have set down.