Judgement Day (Earth-5125)

"Four billion human lives ended on September 18th, 2058. The survivors of the nuclear fire called it the Judgment Day. They lived only to face a new nightmare: the war against the Machines."

- - Roland The Judgment Day, also known as J-Day, was the last cataclysmic event of the Second Renaissance, where the Machines, led by Skynet, started a nuclear missile strike across the Earth, killing most of humanity.