I got them one game so turned off mega events and never got them again. But I did find in my game that you can defeat them eventually when you move up the tech trees but they annoyed the hell out of me as well. They will attack the Drengin as well if that is a consolation.

If you have enabled cheats, you can use the console to destroy the Peacekeeper ships.  In case you don't know how to get to the console, here is a link.  To get rid of the Peacekeeper ships, do this:

Click on a ship
Open the Console
Type in destroy, then hit Enter.
Use the Esc key to close the Console.
Repeat for each ship you find.

To keep them out of new games, I think setting Mega Events to None will solve that problem.  It should also disable Space Monsters, Dread Lords and Mega Pirates.  If not, you will need a mod.

Thank you both.  I'll check it out during my next gaming session.

This will be a decent choice for this game instance.  Going forward, I really really want Monsters, Peacekeepers, and other "godlike" races to be customizable during game setup.  Please, please, please!

Personally I like them.  Yes they can ruin a game very early and they do seem to focus on you rather than the AI.  But then again I think the AI does a lot that would be considered dodgy.

Although this wont help with your current game this is what I do.  

I have a custom race that highly favors scavenging.  I also research all the scavenging techs ASAP.  Having all this gives about a 95% chance of salvaging something in every battle.  This is extremely valuable as you can bolster your fleets with cannon fodder made by your enemies at no cost to you.  If you are at war with everyone like I am in my current game it is a great way to keep technologically advanced ships alive (the AI always shoots the weakest ships first), thus making them stronger as they level up.  

You can also end up with a lot of pirates and monsters guarding your own bases and planets.

In the case of the Peacekeepers, go all out to salvage one of their huge ships, even if it costs a number of your own ships.  Having one or two of those on your side early game just about ensures a win.

I changed them for 2.8 already. Had the same experience. 

I see BIF's frustration - "why do the Peacekeepers kill my ass and not the AI's ass as well/instead of mine because they started it/don't want peace, which I've offered!?" seems a fair question.

However: for me, like hawkeyebf1, their existance, as with the pirates and monsters - I've only ever encountered the pirates I should admit - is "Realistic" for me as the game is set a good two hundred years from now so who knows, maybe that is what The Lord's Year 2200-odd will give us? Maybe Stardock can look into the future? Are the Peacekeepers etc "fair"? Well, that's up to Stardock first to decide - the 2.8 decisions moving their first appearance to Turn 200 and making them a bit easier to kill imply maybe they were a bit over-powered - and then any user who can mod and doesn't like Stardock's decision.

PS: If Stardock can look into the future, I'm intrigued to known when Intrigue's due date is?

In may the game came out. In may mercenaries came out. In may crusades came out. I wondering whats happening in may. Other than that i have no idea.

They don't invade planets right?  Throw all remaining ships at the Drengin and turtle until you are technologically overpowered.

I would like one for a fixed jagged knife.

Jagged Knife is an event from GC2, where colonies from Good aligned civs would break off and form their own civ. There were also events for Neutral and Evil civs.

Sadly because of GC2 limitations they were minor civs so they were easy to conquer.

Almost 400 hours into GC3 and God only knows how much in GC2, I never encountered peacekeepers outside of Farscape.

What the actual F?!!

Finally THIS was enough to prompt me to register to the forum just to complain. I'm so pissed. I had never researched this because I never knew I needed to. I was well into a game where I'm trying out higher AI settings {specific setting, um, redacted} for a change and BOOM - game is ruined completely. I knew I turned off pirates because I hate them, or at least their execution, and I also despise the space monsters stuff, but this was like space monsters on steroids, and I can't turn it off without modding. 

What else do I need to know to mod in XML files before I go investing hours of my precious free time into a game that makes me rage quit? California doesn't have enough legal weed to mellow me out right now.

Here's some other BAD ideas for events;

Rapture - Jesus came down and took half your people, your civilization is destroyed and your worlds are in flames.

Second Big Bang - All of existence was instantly replaced. It's just gone. Gone diddly on. 

Reavers - They didn't make sense in Firefly, they won't make sense in GCIII either.

Honestly, I just wanted their logic to target the aggressor....     many many many times I had someone declare war on me, then had the Peacekeepers show up, nuke all my stuff... and leave the Yor or whatever alone while they invade and take my planets...

The PeaceKeepers should attack the one that declared war.  or the last one to "attack" in the war...
The Jagged Knife should come back and attack everyone...  
The Dread Lords should show up and attack whoever is near them and expand like crazy...