The Expanse Wiki
The Expanse Wiki
Book-icon-simple.png Books war Tv icon.png TV war

The UN-MCR War was a conflict fought in the Sol System by forces of the United Nations Navy (UNN), United Nations Marine Corps (UNMC), Martian Congressional Republic Navy (MCRN), and Martian Marine corps (MMC), serving as the culmination of decades of tension building up in the Cold War and a conspiracy conducted by Protogen to cause a conflict. The fighting centered primarily in the Outer Planets - most notably the Jovian system, although fighting was also conducted amongst the Inner Planets.

The war saw the destruction of dozens of military vessels, the near-collapse of Ganymede Station, the destruction of the city of Goias Maior on Earth and several million civilian casualties, alongside the removal of Esteban Sorrento-Gillis and Sadavir Errinwright from power in the UN (United Nations). The UN-MCR War was the first major interplanetary war fought by humanity.

Prelude to war[]

Previous events[]

Main article: UN-MCR Cold War (TV)
Spoiler-war.png“You can't go home” —  Spoilers for "Season 2" follow.

The UN and MCR (Martian Congressional Republic) had been mutual superpowers in the Solar System for decades prior to the war, with tensions escalating constantly. However, these tensions came to a head following the destruction of the Canterbury and the sequence of events that followed. In the space of a few weeks, the MCRN flagship Donnager, would be destroyed by an unknown class of stealth warship, which the MCR and the Outer Planets Alliance (OPA) believed were constructed by the UN. In reality, however, these events were orchestrated by a web of conspiracies involving Jules-Pierre Mao, Sadavir Errinwright and Pyotr Korshunov, following the discovery of the Protomolecule on the Cronian (Saturnian) moon of Phoebe.

The Eros Incident would cause Earth to launch half of its ground-based nuclear weapons arsenal in an attempt to stop the asteroid colliding with the planet, though the missiles would end up being diverted off-course, with the majority being self-destructed and a handful being stolen by Fred Johnson and the OPA.

Following the Eros Incident, MCR and UN ships would be dispatched to Venus to investigate the Eros crater site, while the MCRN Scirocco and the UNN Nathan Hale would be dispatched to Phoebe, the latter a response to the deployment of the Scirocco. The Nathan Hale would be deployed alongside the widespread deployment of UNN forces to their bases in the outer planets, as to prevent the deployment of a warship to Phoebe from looking suspicious. Ultimately, however, the Scirocco would use its missile payload to destroy the moon to prevent the UN from taking control of the moon. In response, the UN would use several missiles to destroy the Martian moon Deimos, neutralising the MCR's deep-radar station there. The aftermath of this escalation would see heightened tensions between the United Nations and Martian Congressional Republic.

Ganymede incident and Project Caliban[]

Main article: Ganymede incident (TV)

CQB (Close Quarters Battle) combat between UNN and MCRN ships above Ganymede.

Following Phoebe's destruction, the Scirocco would be sent to the Jovian moon Ganymede, to help secure the MCR's position there. A Protomolecule Hybrid would be released onto the surface of the moon by Project Caliban to prove the super soldier's strength in fighting UN Marines and MCR Marines. The confusion caused by this skirmish would ignite the already-heightened tensions around the Jovian moon, leading to an orbital and surface engagement that would leave the MCRN in control of the moon and only one survivor on the moon's surface ; Gunnery Sergeant Bobbie Draper.

For several weeks, the MCRN would control the moon as refugees fled the collapsing Ganymede Station and aid ships attempted to help the station rebuild, though these efforts would eventually be impeded due to the MCRN's implementation of a no-fly zone around Ganymede with authorisation to shoot down anything that interfered with this order while peace talks between the UN and MCR were in progress in New York City. However, these negotiations would be simply a distraction implemented by MCR defence minister Pyotr Korshunov to buy time for the MCRN Karakum to land on Ganymede and take control of Project Caliban materials.

The ship would be shot down by UN forces acting on the orders of UN Undersecretary Sadavir Errinwright before it could reach its destination, while Korshunov was simultaneously assassinated to ensure that the only ones who would be able to secure the Protomolecule as a weapon would be the UN. These events would lead to the re-ignition of fighting in the Jovian system, with the conflict eventually spreading across the entire system. To further inflame the situation, Sergeant Draper would seek asylum on Earth upon discovering the MCR's involvement in the Protomolecule conspiracy.

Declaration of war[]

War would be officially declared by the United Nations following the renewed fighting around Ganymede. Before this relations would further deteriorate with the death of MCR defense minister Pyotr Korshunov, with the Martian Congressional Republic accusing the United Nations of assassinating one of their ministers[1]. Errinwright manipulated Secretary-General Esteban Sorrento-Gillis to finally declare war.

With the UNN Jupiter Fleet engaged around Ganymede, the UNN 5th Fleet was deployed in a hard burn to reinforce the 3rd Fleet, though the MCRN were successfully able to destroy ten UNN ships, forcing two to be scuttled and leaving seven to stay engaged with the MCRN.[2]

Bringing the conflict to the home front[]

Main article: Nuclear strike on Earth

A single MCRN "Planetbuster" deploying its payload of twenty nuclear warheads at Earth.

With the UNN 5:1 ship advantage rapidly reduced to 3:1, the UN began seeking alternate means of reducing the MCR's ability to fight - a lucky discovery by a UN spy satellite Watchtower-14 was able to provide the UN with the potential locations of five MCRN Stealth C Ballistic Missile Platforms. With each platform capable of carrying twenty "Planetbuster" missiles, each loaded with 20 nuclear warheads, the UN were presented with the opportunity to remove the MCR's MAD (Mutually Assured Destruction) first-strike ability to launch nuclear missiles at Earth.

Initial estimates on the success of the strike were placed at 82%, which Secretary-General Sorento-Gillis deemed too low and ordered a cancellation of the strike. Later estimates would up the certainty of a successful attack, leading to the Secretary-General to authorise the strike; however, a malfunction would occur in UNN railgun platform 5, the weapons in which the UN was using to destroy the Martian platforms, leading to the gun firing after its intended time - this delay of a few seconds would provide enough time for the stealth platform to launch a single Planetbuster before its destruction. Although Earth's planetary defense grid would be able to destroy the wide majority of the warheads, one was able to successfully evade the defense grid and impact in near Goias Maior in Amazonia, killing at least two million civilians in the immediate detonation.

Pursuit of Chrisjen Avasarala[]

Main article: Attempted UN asassination of Chrisjen Avasarala

Avasarala, Ghazi and Draper preparing to storm the bridge of the Guanshiyin.

To cover up his involvement in Project Caliban and the Eros incident, Errinwright would accuse UN Deputy-Undersecretary Chrisjen Avasarala of being complicit in the conspiracy to weaponise the Protomolecule, leading to her being branded a traitor. At the outbreak of the war, Avasarala was aboard the Guanshiyin, meeting with Jules-Pierre Mao to discuss the Protomolecule project. Upon discovering the news of Korshunov's assassination and the destruction of the Karakum, Mao would evacuate the yacht aboard a shuttle headed for Io while a Leonidas-class battleship purposed to escort Avasarala was ordered to destroy the Guanshiyin, along with Chrisjen, form direct orders of UN Undersecretary Errinwright.

Avasarala and Roberta "Bobbie" Draper would escape aboard the private racing pinnace Razorback while Cotyar Ghazi would escape in a UNN L-type dropship. Realising that the UN had turned on her, Avasarala broadcasted a distress message on MCR channels via Bobbie's Goliath powered armor suit, preferring imprisonment by the enemy over execution; the signal would be picked up by the crew of the Rocinante with its Martian IFF (Friend or Foe identification) system. The formerly-MCRN Corvette-class light frigate would use its remaining munition supplies defending the Razorback from the battleship in pursuit while Cotyar's dropship would be picked up by the UNN Agatha King, under command of Admiral Michael Souther.

Upon hearing the news that Avasarala's personal spy had been captured aboard the Agatha King, Fleet Admiral Augusto Nguyễn, personally complicit with Errinwright's conspiracy, would personally venture onto the ship to interrogate the prisoner. The Agatha King, now under Nguyễn's command, would then be diverted to Io, to take control of the Protomolecule project as ordered by Errinwright.

Raid on the MCRN Kittur Chennamma[]

Main article: Kittur Chennamma

The Rocinante approaching the damaged Kittur Chennamma in a battle debris field.

While en route to the Jovian moon of Io, the Rocinante would come across the wreck of a Morrigan-class patrol destroyer, the MCRN Kittur Chennamma, severely damaged in battle with UNN forces. The Roci's crew would board the wreck in an attempt to secure fuel and supplies to restock their PDCs and torpedoes. The Roci crew would then rescue three MCRN survivors from the Kittur Chennamma, who would attempt to commandeer the frigate themselves to be put to use in the war. However, they would ultimately fail in their attempt.

The crew of the Rocinante would then partially repair the Kittur to allow the MCRN personnel to return to their fleet, with Avasarala providing Ensign Sinopoli with a copy of Errinwright's message to give to MCRN fleet command with the aim of relaying it to Admiral Souther.

Mutiny aboard the Agatha King and end of the war[]

Main article: Io Campaign (TV)

The MCRN Hammurabi approaching Io, confronting the UNN Third Fleet in the distance.

With MCRN forces pulling back from Saturn to regroup at their shipyards on another Jovian moon, Callisto, UNN fleets including the 3rd, 5th and 8th were converging near Callisto, in what was appearing to be the single-largest fleet battle in history. The MCRN 3rd Fleet was able to exert significant damage on the UNN fleets, but at the cost of four battle groups, leaving the UNN with nineteen destroyers heading to the moon, for a total of fifty-one UNN destroyers facing off against the MCRN's remaining twenty-three.[3]

Upon learning that the Agatha King was headed for Io instead of Callisto as would be expected, the MCRN Hammurabi under the command of Captain Sandrine Kirino diverted its course away from Callisto to intercept the UNN Jupiter Fleet flagship. With the Martian assault cruiser aiming to intercept the Agatha King, Admiral Nguyễn ordered the UNN fleet to instead rally at Io. Although the Hammurabi was a much smaller Scirocco-class assault cruiser facing off against a praised Truman-class dreadnought, the superior technology of Martian warship meant that it would be able to fire at the Agatha King long before the battleship could fire back, giving the cruiser an advantage were it to come to combat. Upon arriving at Io, Nguyễn was able to transfer control of the Hybrid pods' launch mechanisms - housed in the Prospero research facility on the surface - to the Agatha King.

UNN Agatha King engaged in combat with ships from the UNN Third Fleet over Io following the destruction of the UNN Jimenez.

With Nguyễn keeping the crew of the Agatha King - including Admiral Souther - in the dark about why they were heading to Io and removing Souther from the Combat Information Center (CIC), the crew of the Agatha King, namely X.O. Lieutenant Shaffer and Lieutenant Mancuso, and began to suggest that Souther forcibly take back command of the fleet. However, it would not be until Captain Kirino of the Hammurabi decided to relay Errinwright's message to Souther that Souther was persuaded to do so, leading a general mutiny against Nguyễn for fighting an illegal war. Nguyễn was shot twice in the stomach, though was able to kill Souther in the midst of his broadcast announcing the mutiny.

With the UNN ships loyal to Souther beginning to fire on the ones loyal to Nguyễn, Captain Kirino would announce that any ship who broadcasted peaceful intentions would be considered to be flying under a flag of truce with Mars. Now-heavily injured, Nguyễn ordered a launch of the Hybrid pods from Io, with the intent of spreading the Protomolecule to Mars. Many pods were shot down by the Rocinante and the joint-fleet above Io, though many more were able to escape the Jovian system and begin heading sun-ward.


The Expanse The formation of The Ring

The Ring is formed by the Protomolecule beyond Uranus' orbit.

One of these pods would impact the Agatha King, spreading Protomolecule onto the ship and infecting Cotyar in the process. Knowing he was doomed, the spy would begin to cause a reactor meltdown of the ship to prevent the contagion from escaping - this would, however, mean that there would be no way to regain launch control of the Hybrid pods heading for Mars. Ultimately, the crew of the Rocinante were able to land on Io and capture or kill everyone involved in Project Caliban, eventually destroying the site entirely with a nuclear weapon. The pods would be intercepted and destroyed thanks to Fred Johnson, utilising the missiles he stole from Earth in the Eros Incident at Tycho Station to shoot down the pods before they were able to hit Mars.

With the destruction of the Agatha King, the ousting of Sadavir Errinwright for treason back on Earth, and the resignation of Esteban Sorrento-Gillis as Secretary-General, the UN-MCR War ended in time to observe the Protomolecule on Venus rise out of the planet's atmosphere and form the Sol Gate Ring beyond Uranus' orbit.



  1. The Expanse TV series - Season 3, Episode 1: "Fight or Flight"
  2. The Expanse TV series: Season 3, episode 2 - IFF
  3. The Expanse TV series: Season 3, episode 5 - Triple Point