WMG / Thundarr the Barbarian

Oblivion is a prequel to Thundarr.
The moon is broken in both. Humanity survived, but doesn't remember the Tet 2000 years later.

It hasn't been 2000 years.
The disaster pretty much screwed up timekeeping. It's actually been far less time - long enough to be a while, but short enough for the ruins of society to look the way they do.

"Prophecy of Peril" was also a Spin-Off attempt.
The episode ends with the three warrior women now in the 20th Century. Earlier in the season they introduced a young girl also in that time frame; this could have easily served as a girl power adventure show from Ruby-Spears.

The "Runaway Planet" did it.
The planet that caused the disaster was actually some sort of Eldritch Abomination which warped the laws of physics around Earth, causing all the magic and general weirdness on display after such a short timespan.