1986VG1 Ulysses

The Ulysses Disaster was a large-scale and catastrophic  between the planet Earth and the remnant meteors of a related impact event between the 5254 Ulysses and a. It took place in July of 1999 and resulted in a major loss of life and land.

Timeline
Sometime in 1986, the 5254 Ulysses asteroid was discovered. The asteroid has an elliptical orbit around the Sun. During this time, it is not expected to be a threat to humanity.

In 1994, scientists discovered that the asteroid was, indeed, a threat. They estimated that in about five years' time, it would impact Polyphemus, a Jupiter Trojan, and result in a large number of meteors that would strike the Earth. This news was eventually shared with the international community.

Between 1994 and 1999, construction was performed on the Stonehenge Type-3, an anti-aircraft railgun network. It was the first of its kind, and the only defense the world had against the meteors.

In July of 1999, the railgun network was put to the test as the impact events began. However, given that there were 10,000 meteors, the railgun network had no chance in taking them all down. Damage to the planet was catastrophic.