Abliarsec

February 14th C.E.70, facing with defeat and failing their strategic goal, Admiral William Sutherland onboard Alliance carrier Roosevelt ordered the Peacemaker Nuclear Task Force to launch, targeting the illegal agricultural colonies of PLANT. Intending to complete their mission of sabotaging PLANTs food production capability no matter what.

-From Gundam Seed RE, the manga. Although it heavily condensed and change the show's event (cutting out alot of content) in order to show off redesigned mechs, the manga did show us the nuclear strike in detail. Showing the desperation of Zaft trying to prevent a nuclear strike on the homeland. Ofc, it is kinda questionable just how "canon" these kind of non-animated stuff is.

February 14th, CE70. Three days after Earth Alliance declared war on PLANT, an Alliance fleet entered Lagrange point 5 space to confront PLANT in February 14th. During a confrontation between the two, Alliance carrier Roosevelt deployed nuclear weaponry. A nuclear missile struck the illegal agricultural colony Junius Seven, shattering the colony to million pieces ina blinding flash, and took the lives of 243 721 people. This act turned the on-and-off skirmishes between ZAFT and Alliance into an all-out war.

February 11th, CE70. Shortly after the founding of the Earth Alliance in the Alaska Declaration, the newly formed Alliance declared war on PLANT on the February 11th, dispatching a large fleet to the colonies, with the intention of subduing the rebellious coordinators.