So my idea is not a tiny fix, but a rather in-depth change to how starting wars would work.  Probably outside the scope of easily applicable changes that devs are looking for from the forums but I like the idea so I'll put it in and hope for the best.

Premise

Your populace would be generally unhappy going to war for no reason and so you would need "public consent" to start war without unhappiness modifiers.  [the amount of unhappiness would vary depending on the military/pacifist leaning of your population]

UI

 I picture this as being represented similar to the diplomacy screen.  A -100 - +100 scale where -100 means your populace wants them wiped from the galaxy and +100 is they are best friends and would become rebellious over going to war with them.  Minor factions would also be represented here.

Natural Scale Movement

Idealy these "Public Opinion Scales' would wander dynamically based on what's happening in the galaxy.  

• Trading partners and allies would create a positive movement on this scale
• Having ships killed in neutral space (especially colony ships) would naturally anger the populace.  
• Having close neighbours while you are suffering from over-population might make people slightly resentful.  
• If I have a peace-treaty with a race and someone else is fighting with them, that would naturally turn my populace against that other (non-treatied) race.  
• Military build-up could also have an effect here:  If you see your neighbours arming up, it could make people nervous.

Things like that, hopefully you get the idea here.

I could also easily see this affecting your military/pacifist leaning in your senate.  If you have neighbours your people hate, they would naturally tend to drift towards militarism (maybe even eventually giving you unhappiness modifiers for NOT going to war).  And vice-versa.

Propaganda

For each faction, you would be given propaganda options to change public opinion about the race.  It might make sense for your government type (and tech) to affect the costs/availability of certain options on this screen.  I can think of a few interesting ones off the top of my head:

• Media Multiplier: Any negative opinion modifiers from this race are doubled for X turns.  Your media sources widely publicize any acts that will make your populace see the Y-race negatively.
• Fear mongering: Decreases public opinion based on the amount of military ships in close proximity to your space.
• False Flag Operation: Sacrifice a ship to reduce public opinion of the "responsible" party.

Targeted races should have a chance to hear about your propaganda efforts based on how inter-connected your races are.  Proximity and trade-status would have an effect here.

Declaring War (this idea is a slightly modified version of Downer's suggestion in a Forced Truce thread)

Rather than giving the opponent a Force Truce option, I would restrict the Declare War option.

• They will cost more the further away from your home system they are.
• The more turns you have to conquer them the more influence it will cost.
• Once you reach the end of your proposed Declare War period, you will have a steadily increasing unhappiness modifier until you end the war.
• Your influence cost would be dramatically scaled relative to your populace's opinion of the target race.  It should be cheaper to use propaganda over time, rather than a surprise declaration of war.
• Relative force would also have an effect.  Much easier to sell a war against someone weak rather than someone stronger than you.

To anyone read the whole thing, I want to thank you for your time.

Interesting! My one suggestion and one critique:

Rather than creating a separate value "Public Opinion," it might be cleaner to just incorporate that into Cold War as a temperature value. The higher the relative temperature the easier it would be to Declare War. 

My one critique it that I would like the opponent to be interact with war in a non-military fashion. So my current thought is, maybe the target of the war can concede the identified Systems and concede them to end the war.

For example, you target an outer system, but end up marching straight to my homeworld. So I concede (not lose) the system that you identify, and the war ends and public opinion goes back to being unfavorable for war (temperature drops). Thematically, it would make sense. You only wanted X systems, so now that you have it you can't use it to justify war anymore. 

*combined not relative

A simple question for you: how would the population of a majoritary militarist goverment be generaly oposed to war (you said it varies with the tendencies, but why allways negative)?

And another one: how would cravers be generaly oposed to war?

other than that ... it seems like an interesting system. Some ideeas could be lifted from here if the entire thing doesn't make it through in one way or another. Other than that, kudos.

Cronstintein wrote:

XDAvenger93 wrote:

A simple question for you: how would the population of a majority militarist goverment be generaly oposed to war (you said it varies with the tendencies, but why allways negative)?

And another one: how would cravers be generaly oposed to war?

other than that ... it seems like an interesting system. Some ideeas could be lifted from here if the entire thing doesn't make it through in one way or another. Other than that, kudos.

Just because you're pro-war (ie: militarist) doesn't mean you neccesarily want to fight with everybody.  I'm sure there are plenty of pro-war Americans who would be against taking over Canada, for instance.

I would expect if such a system were put in place, that there would be racial modifiers. Cravers could be more prone to having negative public opinion on nearby races and would thus reduced costs for starting conflicts.

I also think this would open the door for public relations type maneuvers where you could suck up to races in the hopes of preventing them from warring with you.

Think of it less as being pro-war versus pro a specific war campaign. Some Cravers might think its a waste to go after X faction or set Y as a military goal. So they always want to go to war, but they value different war campaigns differently.