Originally Posted by
thedukelamere
In a nutshell; Episode 3 doesn't go in the good guys favor. Bran wargs into the past, first trying to warn the Mad King of the threat of the WWs and to better prepare the defenses in King's Landing. This turns the Mad King Mad and basically Hodor-izes him i.e. "burn them all." Since time is a closed loop and it doesn't work, he travels further back to work with his ancestor Bran the Builder and create the wall. Then he goes alllllll the way back to try and reason with the Children who are about to create the Night King, warging into him so he can speak directly to them. He stays too long and the "it's beautiful under the sea, but stay too long and you'll drown" idiom comes full circle, trapping Bran in the Night King forever.
I don't know if I buy it, because it creates a few too many Back to The Future issues from them existing at the same time, but it could explain a few of the goofy "why did the WWs bring 1000 ft chains with them to dredge Viserion" questions.