The year is 174 AG.
The Red Lotus has been defeated. Its leader, the airbender Zaheer, rots in jail and his allies were killed in battle. But while they failed to destroy the avatar, they left a very large mess.
With the Earth Queen dead, suffocated by Zaheer, her Kingdom has fallen into chaos, splintering as various local warlords fight for control. Having died childless, Hou-Ting's heir is her nephew, Wu. But Wu is underage, and does not command the authority necessary to stitch the realm back together. To make matters worse, one of Hou-Ting's brothers has himself claimed the throne and wages a brutal civil war. To stop him, a former guard from the metalbender city Xaofu, Kuvira, has been appointed to the role of regent, but even as she pushes to end the war and return peace and stability to the Earth Kingdom, she has grander ambitions- and thanks to a mysterious superweapon she is developing, she may succeed.
Meanwhile, the other nations look on with concern, particularly the Earth Kingdom's closest neighbour, the United Republic of Nations, where elections are soon to be held. It is by far the youngest of the five nations and was established on Earth Kingdom territory. Avatar Aang made it an independent nation rather than return it to the Earth Kingdom, but many within the Kingdom long for the return of the territory. They view it as a relic of Fire Nation colonialism, a wrong to be righted. As Election Day in Republic City draws closer, the President has authorised a referendum on closer ties with the Earth Kingdom to settle the matter publically.
Amidst all of this, the Avatar is missing, having vanished in the aftermath of the fight against the Red Lotus. Without her, her friends have drifted apart, but with Kuvira drawing ever closer to undisputed power it may be time for Korra to return.
Once again, the world needs its Avatar.