Invasion of the United Republic of Nations

The annexation of the United Republic of Nations was the final and pinnacle event of the formation of the Earth Empire. It took place in the area controlled by the United Republic of Nations.

Prelude
After the liberation of the Beifong family and the escape of Zhu Li, Kuvira ordered for the final faze of her plan for domination over the Earth Kingdom, the annexation of the United Republic of Nations, land that to her, was rightly Earth Empire territory. She modernized her superweapon, upgrading it with a giant mecha suit, for easier transportation. That night, Kuvira's army stepped onto Uniter Republic land and started the invasion. A single outpost saw the army approaching, but it could do little, as Kuvira's superweapon fire and destroyed the compound.

When Bolin, Zhu Li and Lin Beifong arrived to Republic City, it was revealed that Wu's plans for evacuating the city weren't going according to plan. The initial evacuation wasn't mandatory, and only 18 families left the city. When the trio briefed President Raiko, he ordered that the evacuation would become mandatory for all residents. Later that day, Mako delivered a speech by radio to the people of Republic City, telling them that they are at war, and that possible conflict and occupation is only two weeks ahead. As the crowds started to panic, Wu stepped in and managed to calm down the fraternized crowd with his calm demeanor, telling them that the right thing to do is to calmly evacuate the city, to show the world that the residents of Republic City are brave enough to handle such a manor. Wu's speech worked, as the phone lines stopped ringing, and the people started to calmly evacuate to the train station and out of the city.

At the same time, President Raiko moved his command center to Air Temple Island, the only safe place in the city. As the communications systems were being installed, Korra, Mako, Asami and Bolin asked the president for permission, to try and stop Kuvira's superweapon from reaching Republic City. As they were searching for the weapon, they were shoched to realize, that the weapon was upgraded. As they were fired upon, they quickly turned and left for Republic City to warn Raiko.

The battle begins
As they reached the city and told Raiko and Tenzin about Kuvira's army's whereabouts, they were shocked, as Prince Wu wasn't finished evacuating the city. At the same time, the United Forces' Battleships entered Republic City harbor, to try to defend the city. Korra latter travelled to the outskirts of the city, to face Kuvira's Army with most of the United Forces's ground forces supporting her. As Kuvira's army came just several tens of feet from them, Kuvira ordered the capitulation of the city. After initially refusing and even ordering her to surrender, Raiko was forced to surrender, when Kuvira showed the sheere power of her weapon, destroying several Battleships in the harbor. When Kuvira ordered the capture of Raiko, Korra managed to get away from the base camp to meet with Asami, Bolin, Mako and the others waiting in a factory, where the  Hummingbird mecha suits were beign produced.

As Raiko surrendered to Kuvira, the latter ordered Bataar Jr.  to go fetch Raiko to negotiate a formal surrender. Korra and the others quickly found out, that the only way to stop the city from falling into Kuvira's hands was to capture Bataar Jr. Korra, accompanied by Tenzin, Bumi, Jinora and Kai, they managed to get to Bataar Jr.'s airships on a flying bison, where they overpowered him and safely brought him to the factory without anyone noticing.

When Bataar Jr.'s airships arrived at Air Temple Island, all the guards and Raiko were shocked, when they found out, that Bataar Jr. was missing. As Bataar Jr. was brought to the warehouse, he was tied up and questioned by Korra and his Mother, on what were the weaknesses of the superweapon. As he didn't want to cooperate Korra threatened him with not letting him see Kuvira ever again. Shocked with this, Bataar Jr. agreed to talk to Kuvira to negotiate a ceasefire. Everything didn't go according to plan, as Kuvira found out the coordinates of the facility and fired upon it.