Book 2 of The Legend of Korra attracts the most criticism from any of the show's seasons. A big contributing factor to the dislike for the season was its sudden and confusing worldbuilding, and much of that centered around the spirit portals that became the focal point of the plot and character motivations. With more than a few magical features, a history spanning millennia and only scraps of information to go off, of it can be difficult to know which way is up or down with these extra-dimensional doorways. Let's take it piece by piece.

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As could be guessed from the name, the spirit portals are doorways into the Spirit World which allow individuals to pass from one to the other freely. Though they never came up in the series prior, the portals were crucial to the second season of The Legend of Korra and became fixtures of the world thereafter. To understand their history, one would need to wind back the clock 10,000 lifetimes to the time of the first Avatar, Wan.

After witnessing a lifetime of animosity between humans and spirits, Wan confined the spirits to the Spirit World to separate them from humanity and closed off the portals through which they traveled. At that time there were two portals, their locations in the material world corresponding to the North and the South Poles on Earth. On the other side, in the Spirit World, the two portals opposed one another with the Tree of Time between them, otherwise known as the prison for the dark spirit Vaatu.

Once Wan closed the portals he established the Avatar as the Bridge Between Worlds, a diplomatic position whereby the Avatar would try to ease relations between humans and spirits as a primary duty they inherited from their predecessor. Among the powers of the Avatar was an exclusive ability to close and reopen the spirit portals during the winter and summer solstice (the time when the barrier between the physical and Spirit World is weakest) although no Avatars since Wan were ever known to take advantage of said ability.

That is until Korra came along and learned of the forgotten Wan, gaining unprecedented insight into the history and nature of the spirit portals. When her uncle Unalaq led her to the portal in the South Pole, she found it surrounded by the Everstorm, an eternal blizzard that raged as a result of spirits unhappy with the spiritual discord in the Southern Water Tribe. Though Unalaq himself turned out to be an evil manipulator conspiring against Korra, he ultimately showed her the importance of reuniting the Spirit World and the human world. Korra reopened both portals during Harmonic Convergence and restored balance to the world.

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The result was a release of energy across the globe that reignited the Air Nation for the first time since Avatar Aang. With Airbenders popping up all around the world and spirits freely traveling into the human world, it was clear that the world would never be the same, but Korra had still greater strides toward unity to make. Unalaq's attack on Republic City as the Dark Avatar unleashed spirit vines across the urban landscape that were fertile ground for spirits, and the vines themselves proved a deadly power source for an energy weapon wielded by the despot Kuvira.

It was in her battle against Kuvira that Korra bent the energy of Kuvira's weapon, unleashing a devastating amount of power which opened a third spirit portal for the first time in history. While the other two portals were confined to the North and South Poles where people rarely traveled, the third portal's location in Republic City united the two worlds more than ever. Ultimately Korra came to embrace the change, and as she reformed the Avatar's responsibility as the Bridge Between Worlds she settled into a new position as an ambassador between them. The bright shining lights represent a new age of harmony, Korra' greatest achievement, and, hey, they're not bad vacation spots either!

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