After War Gundam X

When one space colony declared its independence from the Earth Federation, the devastating 7th Space War, an all-out war between Earth and space, resulted. The Federation responded to the Space Revolutionary Army with mobile suits, called Gundams. However, the Space Revolutionary forces played their trump card and dropped hundreds of space colonies onto the Earth, plunging the planet into a seven-year-long nuclear winter. (myanimelist.net)