I have have used 'Eternal War' trait twice with an edited race.  In my first game I could make peace treaties until I had militarists faction in the senate.  Which is fine.  But once the militarists were no longer in the senate, I still can't make peace treaties.  I then started a game with a friend through steam and again chose the 'eternal war' trait.  In this game there has been 2 elections and the militarists have never been in the senate.  However, I still can't make peace treaties.  Here are the 2 files that I have on it.

tim john.sav

Luminaris.sav

Oh nice, I was about to post exactly the same question here!

I have a custom made race, an authocracy, with 'eternal war' trait, but not militarist people, industrialist.
In the single leading party, there is an industrialist leader present, no militarist.

Still the peace option is unavailable to my people!

I mean it will be hard to avoid a militarist push to power in later stages of the game, since construction of ships increases military support, but currently industrialists are at 90-95%.