I have no idea. I always seem to get that as well.

And you're right. I am 'militaristic' even if the only ships I have are constructors, and I have only 9 or 10 planets.

Makes no sense at all.

Great research, qrtxian!

One thing I had considered testing, but never got around to it, was the relative values for racial traits of defense or offense.

That is, I had intended to set up a series of 2-race sandbox games in the smallest galaxy, use pre-set make-up races, and iterate the values of those traits.  Real life intervened, and (as i said) I never got around to it.

Tough difficulty - I'm about ready for Painful but haven't played any games yet - on DL (alliances may be harder or easier on the expansions); generally, mid to late game as it's usually after I've researched all the diplomatic techs up to Majesty or higher. In my experience, enough pluses can outweigh a minus, but the more I play, the more random alliances seem. I've had AIs who top me in every category become Close and ally, and I've had weak AIs who I could easily crush never ally despite a lack of any minuses.  I've had a few games as a good race that dragged out for years after the last major threat went down because I was roleplaying my alignment and trying to get a diplomatic win. Were I less patient I probably would have wiped out the remaining unallied AIs in a lot of those games. Keeping good relations with an AI is largely a matter of skill, but actually getting an alliance seems to require a healthy dose of luck.

How aggressive are those militaristic Pacifists in play, I wonder? (Edit: Actually, "militaristic pacifists" sounds a lot like the Peacekeepers mega event, when I think about it).

If you mean Peaceful (Aggression), that's available in DA as well (unsure about DL), and I'm still getting Militaristic races.  Like, 80% of the time, even.

If it's something else, please enlighten me.

I'm fairly certain that adjusting an AI's aggression will have no effect on whether they have the "- Militaristic" penalty in diplomacy, which is what Sole Soul is talking about. I can't be absolutely sure as it's not an option in DL, which is all I have.

As far as dealing with it, if it's really harming your ability to form alliances, my only solution would be to buddy up with the races that don't have it - there's always at least one or two, and I'm almost certain it's not "contagious" as the OP says. Probably all the races without were being killed off. That said, it really doesn't seem to make a huge difference to my games - the last time I focused on befriending the 'non-militaristic' races, they all declared war on me and died and I wound up winning in an alliance with the Terrans, Yor, and Korx, all of whom had the "militaristic" penalty. As I said before, alliances seem random like that.

After loading up TA, and adjusting the Aggression slider to 0 for the Drengin it did indeed result in a + Peace-Loving stat to be placed in the Relations screen.

My guess is that the numbers from TA were in DL/DA "under the hood", they were there and could be altered slightly by events/discoveries/tech/gameplay but usually not big enough shifts to say change a Militaristic into Peace-Loving (e.g. The Drengin start with a 70 aggression level; I'll have to check the exact number but I'm pretty sure that it has to be under 40 to be considered peace-loving)

So its much easier for a race like the Altarians, which start in the 40s, to become militaristic, than for the Drengin to become peace loving.

Yes, as best as I understand it, the "militaristic" trait is randomly determined at the beginning of a new game and has nothing to do with the race's aggression slider.

Edit: Silverbeacher, what events are there that change a race's aggression? The only one I can think of would be the "ethical reversal" event where an evil race becomes good or vice versa. I don't know for sure it does, but it seems logical (one thinks good Drengin would be less warmongering).