One Year War

The One Year War was the first major conflict of the Universal Century timeline, fought between the Principality of Zeon and the Earth Federation from January 3, 0079 to January 1, 0080. Mobile Suit Gundam, 08th MS Team, and 0080 all take place during the One Year War.

Causes
The One Year War was a culmination of the hostility between Side 3's Principality of Zeon and the Earth Federation. Relations between the two had been tense since Side 3 declared themselves the independent Republic of Zeon under the leadership of Zeon Zum Deikun in UC 0058, and had only worsened since Deikun's death and the Zabi family's rise to power in UC 0068. Declaring themselves the Principality of Zeon a year later, and brutally purging Zeon Deikun's remaining followers, the Principality became increasingly hostile to the Earth Federation. In October of UC 0078, the Zeon entered a state of national mobilization, dividing their military into a Space Attack Force under the command of Dozle Zabi and a Mobile Assault Force under the command of Kycilia Zabi. Three months later, in January UC 0079, the Principality of Zeon declared open war on the Earth Federation.

Overview
The One Year War was the single largest and most devastating conflict of the Universal Century, in both the number of military casualties, civilian deaths, and devastation across the entire Earth Sphere. It began on January 3, UC 0079, when the Principality of Zeon launched surprise attacks against the Earth Federation controlled Sides. During the fierce fighting of the first month of the war, weapons of mass destruction were used indiscriminately, with Zeon forces deploying poison gas in inhabited colonies, attempting a colony drop against the EFF's headquarters at Jaburo during Operation British, and both sides using nuclear weapons during the Battle of Loum. During this period of fighting, billions of Earth Federation civilians were killed, wiping out approximately to a third to a fifth and 3 forth's of humanity in less than a month. After this, both parties agreed to sign the Antarctic Treaty which, among other things, forbid the use of weapons of mass destruction.

With the Earth Federation Space Forces devastated, Zeon pressed its advantage by staging an invasion of Earth, dropping mobile suit forces onto the planet during several operations in March of UC 0079. This began a long stalemate period between the Earth Federation and the Principality of Zeon, with the Earth Federation slowly giving ground until the Zeon had control over approximately two thirds of Earth's surface. In September, the Earth Federation's Operation V was scheduled to undergo secret testing in Side 7, but was discovered by Zeon forces under the command of Char Aznable. This marks the beginning of the events of Mobile Suit Gundam.

The turning point of the war was in early November, when the Earth Federation launched Operation Odessa, a counteroffensive against Zeon forces in eastern Europe. Using almost entirely conventional forces, the Earth Federation was victorious, successfully defeating the Zeon, forcing much of their force to retreat or surrender. Soon after, the Earth Federation launched its counteroffensive into space, attacking first the Zeon Space Attack Force headquarters at the Solomon asteroid base on Christmas Eve, December 24, and then defeating the Zeon forces gathered at A Baoa Qu on New Year's Eve, December 31. After Zeon's defeat at A Baoa Qu, Zeon officially surrendered, ending the war on January 1, UC 0080.

The One Week Battle
The Principality of Zeon launched a surprise attack against Side 1, Side 2, and Side 4 on January 3, UC 0079. Attacking a mere three seconds after officially declaring war (a fact that was sardonically referred to as the "three second warning"), the Zeon used their mobile suit forces to eliminate Earth Federation Space Forces resistance before killing the civilian inhabitants of a some colonies of with poison gas. In this manner, approximately unknown amount of   are killed Spacenoids were killed by Zeon forces. This period of initial slaughter became known as the One Week Battle or One Week War. It was during this time that Side 6 declared its neutrality in the conflict.

The peak of the One Week Battle was Operation British, which took place on January 10, UC 0079. Zeon forces used the depopulated colony cylinder Side 2, Bunch 8 Isle Iffish in an attempt to destroy the Earth Federation Forces main headquarters, Jaburo. Though the Earth Federation Space Forces dispatched a fleet of their surviving warships in an attempt to stop the operation, the Zeon military successfully defended the colony and the EFSF was forced to withdraw after taking near total losses. Upon entering the atmosphere, however, Isle Iffish broke apart, missing Jaburo but causing widespread destruction across Earth. The largest remaining piece of the colony, consisting of approximately the entire front half, hit Sydney, Australia, completely wiping out the city and causing massive damage across the entire continent.

The Battle of Loum
After the failure of Operation British, Zeon forces attacked Side 5, also known as Loum, on January 15, UC 0079. Beginning as an attempt to drop a second colony, the operation quickly turned into a full scale fleet battle when the majority of the surviving Earth Federation Space Forces, commanded by General Revil, counterattacked. Both sides used nuclear weapons in this battle, causing horrific loss of life not only among the combatants, but resulting in complete destruction of Side 5 as well. The Earth Federation managed to halt the attempted colony drop and inflict significant losses on the Zeon, but they were unable to prevent the destruction of Side 5 but they were able to evacuate few million of it's inhabitens before the battle begin, and their forces were annihilated during the battle. The Battle of Loum marks the first time that mobile suits showed their true potential in combat, proving to be viciously effective against the Earth Federation fleet. General Revil was captured by the Black Tri-stars, and several other Zeon aces (most famously the Red Comet) first made a name for themselves during the battle.

The Antarctic Treaty
After the atrocities of the One Week Battle and the Battle of Loum and with count varying apon varous gundam sources it could of been almost with to a half to a fifth and 3 forth's  of man kind dead but most likely a near third or forth dead, the Earth Federation and the Principality of Zeon agreed to meet  in Antarctica in order to discuss terms of peace. The Earth Federation, and most of the space forces that can move wiped were wiped out at loum and a few billion of its citizens dead in less than a month, was ready to consider surrendering to the Principality of Zeon. However, during the talks, General Revil escaped from Zeon custody and returned to the Earth Federation, giving his famous "Zeon is exhausted!" speech detailing poor condition of Zeon's military after the heavy fighting. In a large part due to this speech, the Earth Federation refused to surrender at Antarctica, instead negotiating for several important agreements. The use of weapons of mass destruction -- including the use of nuclear and chemical attacks, as well as colony drops -- was forbidden, rules for the humane treatment of POWs were agreed upon, and the neutrality of uninvolved parties such as Side 6 and the Jupiter Energy Fleet was guaranteed.

The Earth Invasion
Upon realizing that the war was becoming a long, drawn out battle instead of a sudden, quick strike, the Principality of Zeon decided to invade Earth. In February they began to organize an Earth Attack Force under the command of Garma Zabi, the youngest member of the Zabi family. Beginning on March 1, the newly formed Earth Attack Force began staging drop operations to land troops on Earth; over the course of the next month, they would stage a total of five drops, landing in central Asia, North America, Australia, and northern African and the Middle East. From these drop locations, the Zeon army spread across the planet, using captured facilities and material (notably including the Earth Federation's massive California Base) to strengthen their military power. Within a few months, Zeon controlled most of Europe, Asia,, and North America.

Operation V
During Zeon's offensive on Earth, the Earth Federation were desperately trying to develop mobile suits of their own. Operation V was a result of this; a top secret Earth Federation Forces research project aimed at producing mobile suits for the Earth Federation, while the Vison Plan was enacted to rebuild the Earth Federation Space Forces. A major breakthrough of Operation V was the development of compact, mobile suit-sized beam weapons, giving a mobile suit the effective power of a battleship cannon. Three prototype designs were completed under Operation V; the RX-75 Guntank, the RX-77 Guncannon, and the famous RX-78 Gundam. Unfortunately for the Earth Federation, while the new Pegasus-class ship White Base was traveling to Side 7 with a number of RX-series prototypes for space testing, they were discovered by a Zeon Musai commanded by Char Aznable. Aznable's subordinates attempted to destroy the Operation V prototypes while on a recon mission inside Side 7, and during the attack the civilian Amuro Ray managed to enter the cockpit of an RX-78-2 Gundam unit. The first ever case of MS vs. MS combat took place on September 18, UC 0079, when Amuro destroyed two Zaku IIs with the Gundam. This point marks the beginning of the story of Mobile Suit Gundam. It also set into motion a series of events that would sent the White Base to Earth crewed almost entirely by civilian refugees. On October 4, Earth Attack Force commander Garma Zabi was killed while leading an attack against the White Base in North America.

Operation Odessa
Operation Odessa was the Earth Federation's first major offensive campaign on Earth. Launched in early November, the objective of the campaign was to capture the Zeon mining facilities at Odessa and drive Zeon forces out of Europe and Asia. The operation was launched on November 7, ending two days later in victory for the Earth Federation. This was remarkable for the fact that the Earth Federation Forces consisted almost entirely of conventional forces, tanks and aircraft, and yet managed to defeat the Zeon force consisting of many mobile suits. The Earth Federation did have a small number of mobile suits at the battle, but they were mainly used in mopping up operations, and contributed relatively little to the battle. Operation Odessa marks the turning point of the One Year War, the beginning of the end for Zeon's forces in Europe and Asia.

Operation Cemballo
On December 14, the Earth Federation launched an offensive into space from their fortress Jaburo. This was the start of Operation Cemballo. Sending their new fleets that were lost into space, the EFSF moved towards the Zeon homeland at L2. Standing in their way was the Zeon defensive line, consisting of the asteroid space fortresses Solomon and A Baoa Qu, as well as the lunar city Granada. On Christmas Eve, December 24, UC 0079, the EFSF fleet launched an attack on the asteroid base Solomon, the headquarters of Zeon's Space Attack Force. Using their Solar Flare System, the Earth Federation was able to take Solomon. When it was clear that the battle was lost, Zeon Space Attack Force Dozle Zabi gave the order to evacuate the base and sortied in the Big Zam to fight a delaying action. He succeeded in allowing many Zeon forces to retreat, but was killed by Amuro Ray in the process. The capture of Solomon marks the end of Operation Cemballo.

Operation Star One
Using the newly captured Solomon as a staging area, the Earth Federation Space Forces continued their offensive toward Side 3 in Operation Star One. On December 30, with the Earth Federation Forces en route to the Zeon asteroid base A Baoa Qu, Zeon leader Sovereign Degwin Zabi approached the EFSF fleet with the intention of negotiating an end to the war. Despite knowing that his father was in the line of fire, Gihren Zabi gave the order to fire the Solar Flare system at the EFSF fleet, destroying a full third of the Earth Federation fleet present and killing both Degwin Zabi and General Revil in the process.

Despite these losses, the Earth Federation continued their attack on A Baoa Qu. They assaulted the asteroid base on New Year's Eve, December 31, UC 0079. With their remaining forces, the EFSF fought against the gathered forces of Zeon's Mobile Attack Force and A Baoa Qu's garrison forces. During the battle Kycillia Zabi executed her half-brother Gihren for the crime of murdering their Degwin Zabi, and took command of the battle herself. In the confusion this caused, some Zeon forces -- notably the Delaz Fleet -- fled before the battle was over. When it became clear that the Zeon forces would lose, Kycillia herself attempted to retreat; however, she was killed by Char Aznable before she could escape.

War's End
After Zeon's defeat at A Baoa Qu, and the death of the leadership on both sides of the conflict, the newly restored Republic of Zeon surrendered to the Earth Federation. The two parties signed a peace treaty at Granada on New Year's Day, January 1, UC 0080. By the terms of the treaty, Side 3 was allowed to keep its independence. However, much of Zeon's remaining military was dissatisfied with the conclusion of the war, and chose to retreat to the Zeon base Axis in the asteroid belt. Still more people, such as the Delaz Fleet, decided to remain in the Earth Sphere, hiding from the Earth Federation with the hope of one day striking back at them. Others groups, stranded on Earth and unwilling to surrender, hid themselves and only emerged years later, during Operation Stardust or the first Neo Zeon invasion of Earth.

Aftermath
The One Year War set the stage for many of the Universal Century's later conflicts. The Delaz Fleet's Operation Stardust was a direct result of renegade Zeon soldier's dissatisfaction with the outcome of the war. The Titans were created to counter this threat, thus setting the stage for the Gryps Conflict. The Axis Zeon faction, which later became the First Neo Zeon, was also formed as a direct result of the One Year War, and their actions heavily influenced the Gryps Conflict and the First Neo Zeon War. Other groups, such as the Second Neo Zeon, are not spawned directly from the One Year War, but can trace their roots indirectly back to the conflict. and for the population due to post gundam 0079 canonize stuff  and comman sense that decanonise the old count of how many people died during the one year war. the sources  point out and concludes that at least 8 billion or above that number, or above the previous number said survived the one year war.

note the number of people that survived depends on the year UC. started