What if the defense tree was linked to civics?
Not sure how much that would achieve. Aside from Vasari with repair bays in the defense tree, it's entirely possible to play an aggressive rush game without touching it. Starbases, perhaps, but by the time you're trying to put up one of those you probably already have ice/volcanic techs, so it's only one lab away anyways.
It could work, but I'd prefer something entirely new that fits the theme of diplomacy, which is why I prefer the pact and espionage suggestions.
Darvin, I believe this and similar suggestions came from you second want which is to make the civic path more dangereous. As you said if you build 2 mil and 5 civic you get crushed. I didn't see this question as simply limited to the diplomacy/pact system. Just for the sake of argument what would you get if the defense/security/fortification techs where made available with a combination of militar/civic labs without any changes to the tech trees.
A civic based Vasari player would have early access to colony pods, merchant cargo bays for their economy. The vasari player would also have early access to disruptor nanites, Phasic trap, reintegration and phase stabilizers.
A civic based Advent player would have early access to merchant docks, evangilization nodes, and induced reference. The advent player would also have early access to shield bestowal, mass dissorientation and meteroid control.
A civic based Tec player would have early access to deep space trade, remote construction and docking booms. The tec player would also have early access to gauss upgrades including meson bolt cannons, safety override protocol, and improved destabalization.
I could see this as a huge benefit when playing unlocked games or locked team games for the player that chooses to build an economic empire first but lags on the military front. IMO the defense techs (tier 4 or higher) are mainly meant to protect the empire, but they require a significant investment in military labs to get to the better techs. If you've laid down 5-6 mil labs you are probably building HC's at this point. I want a solution that allows me to focus on the civic path but lay down signficant defenses (fortification) to protect my investment before I go military if at all.
I also see this as being useful possibly for the player in the suicide position. Currently, if you want to starbase you MUST lay down 2-3 military labs. If you are successful and you run your colonizer cap you are limited to asteroids, terrans and deserts. However, if you could lay down 2-3 civic labs you have access to volcano, ice and culture. Of course this only works if repair bay is moved to defense for all races (as stated above).
Tactical starbase support may be more fun too as you can drop in more useful starbases in allied or enemy territories. For example you can siege with an advent starbase. Remote construction with a TEC base/Docking booms or maybe improved destabilization, etc.
And frankly I'm looking for a reason to research advanced techs past the initial 2-4 labs needed to research trade and culture, lrm's and carriers. We already know you can win most games by building 3 military labs and 3-4 civic labs with minimal research in either. Lets have some fun using some of the defense techs that are rarely used because of the need to go full military.
BTW, you will also need alot of civic labs to get the really useful pacts.
TEC - Trade (4), Missle (5), Siege(6), Armor (7), Supply (8)
Advent - Culture (4), Antimatter (5), Beam (6), Anime (7), Shield (8)
Vasari - Resource (4), Phase Jump Drive (5), Nano Tech (Hull regen) (6), Structure (Hull%) (7), Armament (Rate of fire) (8)
Edit - fixed vasari 6,7,8 pact comments
