Chorus

"We crashed in the middle of nowhere, on a planet in the middle of nowhere. Fucking beautiful everybody."

- Grif in FAQ

Chorus is a small planet, long forgotten by the UNSC after the Great War between the humans and the aliens, located on the far edge of colonized space. Since the UNSC had no influence or jurisdiction over the planet, the people of Chorus attempted to rule themselves, but this went rather poorly, and it very quickly led to the onset of a civil war. The planet first appears in the Season 10 finale, Don't Say It and serves as the main setting for the Chorus Trilogy.

Overview
Prior to its appearance, Chorus was one of the last colonized planets before the Great War started. According to Felix, the planet was originally of interest to the UNSC due to an abundance of alien artifacts left on the planet. However, due to the war, the UNSC eventually forgot about the planet, leaving those on Chorus to govern themselves. Eventually, this led to a civil war between the New Republic and the Federal Army of Chorus. When the Reds and Blues crash landed on the planet, both factions sought for their help and skill, believing them to be the greatest military soldiers in the galaxy. Upon discovering them, the two factions came to the conclusion that the Reds and Blues would be the "key" to how the war would end.

Role in Plot
During the flight of a UNSC ship heading toward Blood Gulch with the Reds, Blues, and Carolina onboard, the ship ripped in two and crash landed in an unknown part of the jungle on Chorus. Realizing they could be stranded there for a long period of time, the Reds and Blues make bases from the ship's wreckage near the crash site, while Epsilon and Carolina leave on a mission of their own. After making contact with Donut with the comm tower they built in S.O.S., the group also unknowingly alerted the New Republic and Federal Army of Chorus of their presence.

The factions planned to use their skills to help their respective factions win the war, assuming that the Reds and Blues were the greatest military soldiers in the galaxy. After the group obtained a "rescue team", Locus and Felix arrived at the their location, trying to convince them to join their side to win Chorus' Civil War. Due to Locus' hostile actions, the Reds and Blues work with Felix before a tense firefight occurs with them against the Federal Army. In the battle's conclusion, Simmons, Grif, Tucker, and Caboose are forced to leave the canyon with Felix's group, while the others are captured by the 'Feds'. The four decide to join the New Republic partially because of the events at "Crash Site Bravo".

Layout
Being a (small) planet, Chorus is portrayed to be massive and have multiple locations, using numerous Halo maps to represent it. Unlike Sidewinder which only had an arctic biome, Chorus is shown to have multiple types of biomes like Earth: jungle, desert, grassland, and arctic. It's also implied Chorus has several cities, as the planet was colonized by humans many years ago. However, due to Chorus' Civil War, some of these locations are left abandoned or under control of one of the two factions. A large cave network also exists beneath the surface of Chorus, which the New Republic uses to remain hidden and move between locations undetected.

Crash Site Bravo
The most known and seen location of Chorus in the series is "Crash Site Bravo", where the UNSC spacecraft crash landed. The simulation troopers have stated that the crash site is in a canyon similar to Blood Gulch, but the canyon itself is within a jungle. The canyon became war torn after the battle in Fire, being altered by several explosions and containing numerous corpses.

Trivia

 * Chorus is represented by several multiplayer maps of Halo 4.
 * 'Chorus' might be a pun of Coruscant, the capital planet in the Star Wars franchise.