|"The Earth Kingdom is no more. And from here on out, this man has no authority."|
|— Kuvira denouncing Earth King Wu.|
The formation of the Earth Empire was a mission led by Kuvira to stabilize the Earth Kingdom following Zaheer's assassination of Earth Queen Hou-Ting in 171 AG. However, after uniting ninety percent of the city-states under her banner and blaming the rule of unsuited monarchs for the disarray of the nation, Kuvira deposed Earth King Wu in 174 AG and transformed the kingdom into the Earth Empire under her leadership. After annexing the remaining Earth Kingdom territories, she intended to take back the Earth Kingdom lands that formed the United Republic of Nations though was thwarted by Avatar Korra and her allies. Kuvira surrendered and brought an end to the empire.
After the death of Earth Queen Hou-Ting and with Avatar Korra incapacitated following her mercury poisoning at the hands of the Red Lotus, the Earth Kingdom descended into anarchy. Tenzin and President Raiko asked Suyin Beifong to stabilize the nation, though she objected the use of military force to spread her ideology and rejected the request. Having learned from the Zaofu matriarch that the hereditary succession of leadership was archaic, Kuvira became disillusioned with Suyin, believing her to be abandoning her nation. Knowing the pain to have been abandoned, Kuvira was unwilling to see the entire nation endure the same fate and shouldered the responsibility of reuniting the Kingdom herself. She departed the city, taking a sizable amount of supplies, a part of the security force, and several of the city's wealthiest people with her.
Uniting a nation
Leading part of Zaofu's security force, Kuvira headed toward Ba Sing Se first and managed to stabilize the capital. Following this success, she was appointed Interim President of the Earth Kingdom by the rest of the world leaders. With a quickly expanding army, she traveled the kingdom for three years and liberated the city-states from roving bandits and criminals in exchange for their loyalty to her. This, which earned Kuvira the moniker of "Great Uniter".
When the Earth Kingdom was ninety percent reunited, Kuvira was invited to attend the coronation of Prince Wu, the rightful heir to the Earth Kingdom throne, where she was expected to step down in his favor, as she had promised the world leaders. However, after receiving the Kyoshi Medal of Freedom, she denounced Wu's authority and dissolved the Earth Kingdom, appointing herself as the leader of what she now called the "Earth Empire", intending to bring about a new era of prosperity for her people. As she and her army later departed from the city, Kuvira commissioned Varrick to develop a technique to transfer the energy from the spirit vines into a battery, desiring to use as a weapon.
As one of the last remaining free states, Kuvira led her entire army to Zaofu in order to force the city into surrendering without a battle, knowing that the other nations were scrutinizing their every move. However, after Suyin declared that she would not surrender, Kuvira gave her twenty four hours to join the Empire or she would take the city by force. That same night, Suyin and her twin sons, Wei and Wing, attempted to dispose of Kuvira via a raid. They were easily caught, however, as Kuvira had anticipated the attack and used Zhu Li as a decoy to lure the trio into a trap.
After hearing of the capture of Suyin, Wei, and Wing, Korra, Opal, and Jinora traveled to the outskirts of the city to discuss the situation. Kuvira warned Korra that she was treading in Earth Empire business and challenged her to a one-on-one duel for the fate of Zaofu, which she managed to win. With the city occupied, Kuvira ordered its denizens to bow to her or suffer the consequences of treason, an order all but Baatar and Huan heeded. The fall of Zaofu meant the entire Earth Kingdom was reunited under the banner of the Earth Empire.
Despite having denounced Wu as the leader of the Earth Kingdom at the coronation, Kuvira still desired to capture him. Her agents in Republic City attempted to kidnap Wu, though found themselves thwarted by Team Avatar.
Within the Earth Empire, Kuvira gave the order to round up and imprison anyone who was either not of Earth Kingdom descent or pledged loyalty to her. Bolin and Varrick, who had defected from her army, came across a group of fugitives and helped them cross the fortified border into the United Republic. The two returned to Republic City, where they warned all the world leaders about Kuvira's plans to build a spirit vine-charged super weapon. To that end, Kuvira and Baatar Jr. had traveled to the Foggy Swamp and started to harvest the roots of the banyan-grove tree.
Threatening the United Republic
Weeks after the annexation of Zaofu, the work on the spirit energy cannon was completed, despite Zhu Li's numerous sabotage attempts. Kuvira intended to mobilize it to reclaim the United Republic of Nations as part of the Earth Empire, as she deemed the territory to have been stolen by Avatar Aang and Fire Lord Zuko in the aftermath of the Hundred Year War. When Zhu Li deserted the military of the Earth Empire during the liberation of the Beifong family, Kuvira enacted her plan a week earlier as she knew Zhu Li had inside knowledge of her plan. To achieve this, she installed the cannon on a giant mecha suit, making it far more mobile than if it had to be transported by rail. She then led her forces into Republic City by breaching the Republic's border, shooting her cannon at the nation's fortified station. After a show of force with the power of the cannon, Kuvira forced President Raiko to surrender.
However, a small resistance force led by the Air Nation and Team Avatar fought Kuvira and her mecha suit for the fate of the city and the Earth Kingdom. The resulting battle caused massive damage to Republic City, but the mecha suit was destroyed, the cannon itself discarded into the Spirit Wilds. Korra chased Kuvira into the Spirit Wilds following the mecha suit's destruction, but the defeated dictator found the disconnected cannon entangled in spirit vines and attempted to obliterate the Avatar with it. The unstable energy beam, however, spiraled out of control after finding a new power source in the spiritual energy of the Spirit Wilds of Republic City. Kuvira herself was unable to hold her footing on the swaying cannon, and was ultimately tossed into the path of the energy beam, but Korra jumped in between her and the beam, using her energybending to deflect it. The abundance of spiritual energy fired by the cannon tore open a new spirit portal in the heart of Republic City and blasted the two women into the Spirit World.
In the Spirit World, Korra attempted to negotiate with Kuvira once again. Korra told Kuvira that they were similarly impulsive. Though the military leader initially dismissed Korra's claims of them being similar, the Avatar told her she understood that her eagerness to unite the Earth Kingdom stemmed from her rough childhood, as she did not want her nation to be as vulnerable as she was. Korra explained how her poisoning emotionally scarred her, which in turn caused her to lose her self-worth and confidence to fulfill her duties as the Avatar.
Upon realizing her wrongs, Kuvira returned to Republic City through the new portal, ordered her men to stand down, and declared the battle to be over. As Lin took her into custody, Kuvira said she was willing to accept whatever punishment may fall upon her, being led away by the Beifongs.
Kuvira's government had come to an end, though her legacy had a profound impact on the world. Although she had fulfilled her original purpose of restoring the Earth Kingdom, Earth King Wu decided, in light of recent events, to work on dissolving the earth monarchy in favor of independent states with a democratically elected government akin to the United Republic.
Although having no regard to and concern in spiritual matters in developing the spirit energy cannon, Kuvira inadvertently created a new spirit portal in Republic City, which brought closer links between the spirit and physical worlds.