By the title you maybe able to tell that I like peacefull relations with my AI friends.
Just because a Minor race is weak and undefended does not mean it is plump for invasion.
Too bad AI does not see it my way.
Sooner or latter in ever game the AI will decide to take out minor races. The morality of the AI could be SUPER GOOD but they will decide that they should wipe out minor races.
Here is my Strategy for dealing with the warmonger AI races.
Since you know they will wipe out minor races be prepared.
I know humans love peace but think of it this way when we control the planets of the minor AI we have really the best interest of these minor races in the back of our minds.
1)Always try to colonize a system in the same sector of a minor race.
2)Build social programs, go for PQ improvements, Moral, then cultural boosting projects first and build cultural starbases in these sectors.
3)Build transporters or combat trransporter
4)If you can not grow the population fast enough send in transporters from planets farther away.
5)When you see the defences of the minor race droping increase you spending.
6)Save you game you do not want the majors stealing the planet of the minor race you are trying to protect but some times they take them out before you are ready.
7)Wait a little for the monor races to weaken.
8)When all minor race planets are undefended, pounce!!
9)Invading if the ratio between the tranport and population is high use the invading technics which will damage social projects but gives human invader and advantage.
10)When you own the Minors planets and try to take them all out the same time. Do not build Military Ships on these conquered planets. The stupid warmonger major AI races which forced you to take out the minor race in the first place is liking going to crash one of thier warships into the newly conquered planets. If this happens and system is not defended nothing happens, if the system has defence ships in orbit the warmongers will declare war on humanity.
Try to keep your ships with attack strength out of a battlezone or you may get the "Will feel we should deal with you now...."
In fact I never build anything but frieghters, constructors, colony ships and (combat) tranporters.
If the AI want to be evil let them do the dirty work.
Keep in mind we are only protecting minor races so when a minor pops up late in the game be friendly. Take them out right away before they can build a defence.
My philosophy has always been that if someone's going to conquer them, it might as well be me. This applies to weak majors as well as minors. I never saw a point in protecting anybody, unless you count giving money/tech/ships to a weaker major so they can keep fighting a stronger major, hopefully prolonging the war.
I have been giving weak empires / minors state of the art warships by the dozens. That really seemed to help those empires in their own defense and would not damage my relationship with any majors.
Sometimes I give everyone free ships when two empires are at war. It was like pouring gas to the fire!