Oh. Um. My world has regular evil armies and the such attacking it. They usually get repelled by the yearly new team of heroes. We currently have an evil space empire attacking. Before that was a fallen angel trying to recreate Earth in his image. The time before that was mythological demons trying to flood the Earth so they could exist there freely. The time before that that was a Machine Empire from another dimension trying to destroy the environment so they could live on Earth. ...And, those are only the most recent few!

[Or in a nutshell, his world ~/= Power Rangers, except that it's been going on for at least 17 more years.]