It is a random event.
I have played 100s of games and never had it.
If you have a save game from the turn before the event, you can always reload the turn. I do that with the Jagged Knife event because it is simply too annoying. (It guarantees a win, but it is t e d i o u s)
On Peacekeepers, I have seen others post that you simply research and wait. Eventually, you will be strong enough and, in the meanwhile, no other AI can do anything either. For example, if you go up in engine tech and miniaturization, you can launch a ship or two and lead them around the galaxy and then you build/launch other ships to do what you want.