The scenes regarding the CotF and the origins of the WW in the show raised several questions for me. Most notably, (1) Why did the WW's end up north of the Wall after the children created them at the Isle of Faces, (2) Who was the man we see being transformed, and (3) Why are the WW presently trying to invade Westeros?
(1) In S6E5, Bran shows us a vision of the children transforming a man into what appears to be an icy, blue-eyed WW. I believe this location was on the Isle of Faces due to descriptions found in book canon. Plus, the landscape appeared green and flat, which would be typical of the Riverland area where the IoF is located. -Put a pin in this because I think it is important to my question (3)- Once he awoke from his vision, Bran learns from Leaf that the children created them to protect the children from men, presumably the First Men who were destroying the weirwood trees. The two now seem to be direct enemies, and I am unsure why. Also, both factions are located north of the Wall (although I'm not dismissing the possibility that some may reside somewhere else in Westeros). So why are both the children and the WW's confined behind the Wall? The only explanation that comes to mind is that both are magical beings, which the First Men distrusted and disliked. That may explain why the Wall was built in the first place, to seal away all of the magic from Westeros. The Wall itself is said to have been made with magic. Fighting fire with fire, I guess?
(2) We see an unknown man tied to the Weirwood tree on the Isle of Faces who is impaled in the chest with a shard of black stone, presumably obsidian. I have read that the actor who portrayed this man is also the actor who plays the Night King. However, I don't believe this man was just some nobody First Man. But as to his identity, I am unsure. Possibly Bran the Builder, but I have no evidence to support that.
(3) In the same episode, we see through Bran a vision of a snow-covered weirwood tree surrounded by stones that are arranged in the same spiral pattern as the one we saw in the verdant pastures of the IoF. However, this location is snowy and surrounded by mountains. This leads me to believe that there is a second tree spiral north of the Wall that is analogous to the one at the IoF. Are they somehow connected? By combining all of the facts we learn through Bran's visions in this episode to this theory, we know that the children created the WW, the WW have their own version of the Weirood spiral, the WW are unable to enter Bloodraven's cave due to the magical protecting it, When the Night's King touches Bran, it gives the WW's the ability to enter the cave, and they do so by indiscriminately slaughtering children, direwolves, and men. But why are the WW's on this warpath to cross the Wall? I think it has a lot to do with the two Weirwood spirals. Before I start this theory I want to point out that GRRM has said that the human heart in conflict with itself is the only thing worth writing about. Certainly he means this metaphorically, but what about literally? When the children stabbed the man on the Weirwood they replaced his heart with obsidian, and changed him into a seemingly immortal and powerful magical creature. There is a second Weirwood spiral north of the Wall. Could the WW's have created this new spiral in order to reverse the magical procedure that the children performed? Now we find the WW's north of the Wall and unable to cross the Wall because of the magic with which it was built. We have seen that the WW's can circumvent the magic that kept them out of BR's cave by branding Bran with some sort of marking. I think this will be how they are able to cross the Wall. Once Bran crosses south, that will break the magic within the Wall and give the WW's free reign to cross into Westeros. But why go south though? I think that it stems from that quote about the human heart being in conflict with itself. The WW's were men and still are. They built their own Weirwood spiral to reverse the process and become men again. It obviously hasn't worked. They just want to cross the Wall to become men once more, and they have amassed a massive army of the dead to see that they succeed.
There is so much book lore that surrounds the Wall, the Others, the CotF, and the First Men that I do not fully grasp, but after seeing the episode "The Door" I cobbled together this theory and I would really enjoy hearing any opinions or criticisms.