Bloody Valentine War (Conflicted Hearts)

The Bloody Valentine War was a major conflict between the Earth Alliance, an alliance of four major governments on Earth; ZAFT, the Military of a nation of space colonies located at L5; and Terminal, a Mercenary-like organization with their allies in the Clyne Faction and the neutral Orb Union.

Prelude
The Bloody Valentine War was caused by a series of events centered around the instability of relations between the Naturals and their creations: the Coordinators, among this conflict however were certain factions that were attempting to establish peace between the two subspecies including Terminal and the neutral Orb Union, meanwhile some factions like Blue Cosmos and LOGOS attempted to ignite war and conflict for various benefits to themselves and their beliefs.

Tragedy of Copernicus (February 5, C.E. 70) & Declaration of War (February 11)
On 5 February, CE 70, a joint peace conference being held at the lunar city Copernicus was struck by a terrorist attack, wiping out the entire United Nations's leadership. The only survivor of the attack was ZAFT Supreme Chairman Siegel Clyne, which lead the Earth Alliance to believe ZAFT had orchestrated the attack. In response, the Earth Alliance issued a declaration of war, on 11 February.

Bloody Valentine Incident (February 14) - The Beginning of the War
Three days later, on 14 February C.E. 70, Blue Cosmos leader Muruta Azrael orders the Earth Alliance to launch a nuclear attack against the PLANTs. The Agamemnon-class carrier Roosevelt deployed a nuclear warhead which struck Junius 7, a PLANT-type space colony in the PLANT's Junius City area, destroying the colony and killing 243,721 civilians. Including Lenore Zala, the mother of Athrun Zala, and Isao Kofun's adopted parents and friends.

The incident was soon infamously called the Bloody Valentine Incident, marking the opening of hostilities between the Earth Alliance and ZAFT.

Battle of Yggdrasil (February 22)
The first major battle of the war was fought near the prewar international space station, Yggdrasil. The battle lasted about a month, resulting in the destruction of the space station.

First Battle of Victoria (March 8)
ZAFT launched an attack on Victoria, hoping to seize Habilis Mass Driver at Victoria as their first target of their invasion on Earth, only to be beaten by Earth Alliance’s tank divisions (most under the command of Eurasian Federation). This marked the only victory of Earth Alliance against ZAFT before the development of the Earth Alliance’s GAT-X series mobile suits (better known as G-weapons or Gundams) and the mass-production of Dagger series, which eventually turned the tide to Earth Alliance’s side.

Trivia

 * The Bloody Valentine War in Conflicted Hearts has a number of minor differences.