Doomsday is also known as End Time, a time period described in the eschatological writings and in doomsday scenarios to both Abrahamic and non-Abrahamic religions.
Doomsday reflects an abrupt change generally not for the better. Many doomsday-type events have occurred, usually with localized effects. If you survived a major earthquake, volcano eruption or perhaps Chernobyl, I'm sure the experience was quite doomsday-esqe. What these events have in common was their unpredictability and as such they would have been difficult to prevent or mitigate.