I just tend to keep everyone at a set strength. Where that set strength is kinda depends on who's got the biggest fleet (spoiler: 90% of the time it's the bloody thoraxians) But I try to make sure everyone is as strong as everyone else. Nobody wants to go to a war they haven't already won. Side effect is that I get nice influence boosts with most races, so when one guy does go to war against another, I go, smash some skulls, and tell the aggressor to chuffing quit it already. Usually doesn't dip my influence with them too much (really it should decimate their opinion of me, after all, I did just murder about 5 of their favourite armadas), and I can quickly get it back with bribes, killing their warlords or otherwise just killing pirates. That's another thing, keep your prisoners. All of them. Hold on to them for dear life. You never know when that influence boost may come in handy. Keeping everyones' environment great is also a must. Even the peltians will go to conquest if they don't like their planet (or, rather, it doesn't like them). Improving relations is nice, but keeping everyone respecting everyone elses strength is more important in my book. I could be wrong of course, but it's what tends to work for me.