What triggered the return of "old magic"?

[Waters Gate]

I think the return for magic is triggered by the same thing's that would usually trigger a winter or summer. I think it has something to do with the position and the behavior of the planet Westeros is in compared to it's sun, and maybe also the behaviour of it's moon.

A few specific and remarkable mentions for Westeros it's moon:

-No moonlight ever touches the stoney halls of the caves beneath the hill where the three-eyed crow lives.

-Benerro jabs a finger at the moon, makes a fist and spreads it wide as Tyrion watches him.

-Tyrion has never seen a bigger moon than the one he sees aboard the Selaesori Qhoran when the ship is sailing too close to Valyria. Monstrous and swollen, it looks as if it has swallowed the sun and woken with a fever.

The last thing is something which happens in our solar system as well, as the moon has an eliptical path around the earth at some times its closer to earth than others, and with that it's tug on the sea is greater to.

[Kuarlos]

I m going with...it never left the planet entirely. There are three sources;

R'Hollor- pyromancy- favours fire- favours destruction- a focus on this brought dragons and the doom of valyria.

The Great Other- necromancy- favours cold- favours death. During the war of the children of the forest and the first men the death and weakening of nature brought the others, the death caused by Roberts rebellion following a gradual move away from the old ways of nature caused this new invasion.

Natural- psychic- favours spirituality, balance and nature. Seems to be genetic, mainly had by the children of the forest, it seems open to those who forgo destruction and death. Something entirely absent from mans Psyche in general.

Magic never left, even the seasons are a battle between the forces in the world, it seemed absent in westeros because they werent following any of these three paths more than slightly, until rhagar caused roberts rebellion, setting death across the land, this coupled with the onset of winter released the great other.

Given Bran was guided to the tree eyed crow and arya made her way to the faceless man it seems they have been targeted by those wielding natures magic.