Bran Stark has seen bunch of flashback during the last episode of Game of Thrones, Those flashbacks aren't useless, they're used...
Bran Stark has seen bunch of flashback during the last episode of Game of Thrones, Those flashbacks aren't useless, they're used to give us an idea of what will happen next on Game of Thrones, and it has something to do with the Night King, and how to fight his Army of the White Walkers.
Bran saw the King Slayer, along with the Mad King, that scene has multiple sides, the first one talking about Jamey and preparing a big episode for him, as it has been always the King Slayer disregarding all the good things he has done so far.
The other side of the scene, is showing us, the audience, the whole battle plan, and how they'll fight the Night King and his army..
Showing the Mad King screaming "Burn them all.."
And a flashback of the wildfire, meaning that they should fight them using the wildfire as a primary weapon and burn them all.
And top of that, Bran also saw Daenerys Targaryen, The mother of dragons, and her Dragon flying high in the sky and what it seems to be his shadow over Westeros.

And not to mention his half brother Jon Snow, is really important in the battle to fight the dead army.
Bran has seen so many visions in a flashback, and there are more theories and explanation for each scene, but I've did my best to focus on the main and the most important ones, that indicate how the battle will take a place.
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