Essentially what happened is there were weapons that could be classified as weapons of mass destruction in space. One of them fired and hit the tower. The hit itself wasn't necessarily serious, but it triggered an auto-purge by the tower's systems which essentially meant everything that wasn't deemed necessary to support the orbital ring got ejected to keep it from falling. This lead to enough debris to reach into space several times falling to Earth and the cities around the tower.
It took several military groups all shooting it down to limit the damage.