The United Forces is the main military of the United Republic of Nations and serves as its first line of defense. Reflecting the multi-national makeup of the Republic, the Forces' troops include firebenders, earthbenders, and waterbenders, as well as nonbending soldiers.
During the battle for Republic City, Tenzin sent word to the United Forces that the city had come under attack by the Equalists. After receiving the tip, a contingent from the United Forces began traveling toward Republic City via a fleet of large battleships led by General Iroh, intending to liberate the large metropolis.
Three days later, the First Division arrived and sailed into the waters of Yue Bay, encountering no initial resistance from the Equalists. However, as they neared the city, the ships were caught off guard when they detonated several naval mines, designed to explode upon contact. Not long after, a large formation of biplanes, invented by Hiroshi Sato, attacked the crippled fleet from above, dropping bombs and torpedoes onto the warships before flying away. The firebenders and earthbenders were able to shoot down several planes with cannons and earth discs, while General Iroh himself was able to dispatch two planes before he was knocked into the water by an incoming bomb. Nonetheless, the battleships were not able to withstand the attack, and soon after, the remaining ships were either sinking or heavily damaged.
However, General Iroh survived the destruction of his division and retreated underground with the help of Avatar Korra. Later on, he used Gommu's previous experience as a telegraph operator to send a message to Commander Bumi. Iroh advised the commander not to approach Republic City until he sent him a signal, instead ordering him to hold position at Red Sand Island, as none of the naval vessels used by the United Forces were armed to take on Hiroshi's new combat planes. The Second Division arrived at Air Temple Island shortly after Iroh, Bolin, and Asami destroyed the Equalist air force.
Six months after the Anti-bending Revolution, Korra requested President Raiko, the commander-in-chief of the forces, deploy them to the South Pole in order to aid the Southern Water Tribe in the Water Tribe Civil War. However, Raiko refused to grant military aid, desiring to resolve the civil war by diplomatic means. Korra subsequently went directly to General Iroh, who plotted to bring his fleet to the south for training exercises as an excuse to engage the Northern forces. However, Raiko, tipped off by Mako, discovered their intent and threatened to court martial Iroh if he disobeyed his direct orders, effectively placing the entire United Forces on lockdown.
When Korra later returned with the revelation that Unalaq intended to unleash Vaatu and destroy the entire world, Raiko again rejected her call for help, keeping the United Forces on high alert in Republic City in order to protect its citizens. General Iroh patrolled the bay with his ships, while the Air Force controlled the sky. When the Dark Avatar arrived, the United Forces opened fire, though their attacks were ineffective against him. Unalaq used his enhanced power to push the battleships aside with his waterbending, while using his tentacles to pull the biplanes out of the air.
In 174 AG, the United Forces were called upon to escort Wu safely back to Ba Sing Se after his coronation as the new Earth King. However, the plan was put on hold when Kuvira rejected Wu's authority and took power for herself.
Weeks later, the United Forces fortified the borders of the United Republic and guarded the rail lines into Republic City as a preemptive defensive measure against an attack of Kuvira and her army. When the threat became a reality, General Iroh stationed his troops, consisting of five battalions of foot soldiers and thirty-five mecha tanks, at the clearing from where Kuvira would approach the city and erected a defensive barrier with barbed wire. When both armies stood face-to-face, Kuvira demonstrated the power of her spirit energy cannon by laying waste to the United Forces' fleet in a matter of seconds. When she aimed the weapon on the infantry, General Iroh requested President Raiko permission to engage, though Raiko denied the request and surrendered the city and the United Forces instead, yielding to the overwhelming power of the cannon.
Several weeks later, the United Forces were deployed by President Raiko to erect a perimeter around Republic City's spirit portal. Their actions were opposed by Avatar Korra and the Air Nation, and although General Iroh sympathized with them, he deferred them to President Raiko, since he was the one who ordered the portal on lockdown.
The navy of the United Forces is split into several divisions: The First Division is commanded by General Iroh, while the Second Division was led by Commander Bumi before his resignation in early 171 AG. The First Division was completely destroyed during the battle for Republic City in 170 AG, and part of the overall navy was again destroyed in 174 AG by Kuvira and her spirit energy cannon.
The design of the United Forces' battleships reflects the multi-national makeup of their crews: the ships' cannons bear the insignia of the Fire Nation, the Earth Kingdom insignia is located on their bows, and the Water Tribe insignia emblazons their hulls. Beyond simple aesthetics, the ships' weapon systems are also designed to maximize their crews' various bending abilities: the cannons act as a guide for firebenders to precisely aim and release fireball missiles, multiple platforms are equipped with stone discs to be launched by earthbenders, and waterbenders are stationed low to the waterline for anti-mine defense.
The crewmen of the battleships wear differently colored uniforms, depending on the type of bending that they utilize: Firebenders wear maroon, earthbenders dark green, and waterbenders blue, while nonbenders wear gray. These uniforms may also be supplemented with caps or light helmets equipped with leather neck guards.
High-ranking officers wear a more elaborately designed uniform: The jacket is colored red and not discriminant of the officer's bending abilities, or lack thereof. These uniforms also include gold trimming, a black belt, and white trousers.
List of known commanding officers
After the Anti-bending Revolution, the United Forces acquired biplanes, which were incorporated into their line of warfare and bore the emblem of the United Republic. The Air Force's only known engagement was their defense against the Dark Avatar during the Unalaq Crisis; one of the biplanes was destroyed in the ensuing battle.
The United Forces has an extensive infantry force, consisting of at least five battalions of 275 soldiers each; two battalions are formed by soldiers hailing from the Fire Nation, two from the Earth Kingdom, and one from the Water Tribes. Following the Anti-bending Revolution, the ground troops were strengthened by at least 35 mecha tanks, divided in five battalions of seven.
- While the United Republic of Nations was still led by the council, The Legend of Korra creators, Michael Dante DiMartino and Bryan Konietzko, described the United Forces as being the World of Avatar's parallel to the United Nations in the real world. However, subsequent to the council's dissolution, it has been described by the newly elected president as "the military of the Republic".
- Prior to confirmation of Book Two: Spirits, an early script for "Endgame" had Asami join the United Forces at the end of the episode.