After establishing my Terran Empire (just Humans with Dictatorship instead of Democracy (grabbed charisma, research and ground battling as extra perks)) as dominant force in southern part of the galaxy (conquered Klackons by the way), I had a very long, very bloody war with the Psilons. Every turn there was a big battle, colony siege or skirmish at some remote-and-just-recently-colonized world. Psilons managed to get mighty Alkari on their side while I forged a technological exchange with Meklar and then recruited the cat warriors Mrrshan into my alliance.
This huge interstellar war was observed by the little Gnolams who, after asborbing Darloks into their fold, where quite content with slowly colonizing barren/radiated/toxic planets and trading with pretty much everyone. In a hindsight, I should've paid more attention to the little trader guys...
So the mighty war with Psilons have lasted from 3115.x to 3134.x, thusly spanning about
90 190 or more turns, with several worlds getting bombed, captured, liberated and then
re-captured, with Antarans sometimes showing up to bomb some planet on either side of the war and even a Space Dragon making a rampage in the galactic backyard, with some random star system exploding into nova because Mrrshans derped and didn't do enough research.
Psilons had bombed several of my Klackon-captured colonies into smithereens while my space marines slowly paved their way into heart of Psilon empire. After ground battle of 64 marines vs 30+tanks (hella fun to watch all that blaster fire and exploding tanks), my space marines conqured Psilon capital of Mentar II.
The war at this point turned the galaxy into a giant mess (ownership looked like four-color checkerboard) and because I was tired of it, I have asked Psilons for peace, who accepted and next turn even asked for trade/research treaties. Alkari weren't happy and kept harassing me, but after I managed to persuade Meklar to stop attacking Alkari, the winged dinos decided to drop the war thing altogether. It was peaceful... for a very brief moment.
Five turns later:
"Gnolam fleets have recently visited Orion system aka they just got all juicy stuff and huge planet to colonize" - my reaction was pretty much 'WHAT??'
Within 3 next turns all this happened:
"Gnolam fleets are attacking [name colony here]" x4 (I lost all the battles, including one when I had 18 ships and battlestation and heavily defended planet against 4 Gnolam Titans and Loknar the Orion)
"Psilon Empire surrendered to Gnolams"
"Meklar/Mrsshan/Alkari make peace/alliance with Gnolams"
Few turns later, while my borders were being overwhelmed by Gnolam forces, there was Galactic Council vote and pretty much everyone still alive (Alkari, Meklar and single-planet-dwelling-Mrrshan) voted for Gnolams and I just voted for them as well because I didn't really see how I was wage, not to mention, win, a rebellion against soon-to-be-formed Galactic Gnolam Republic.
And so, in the end, several badass empires were utterly curbstomped and out-diplomacized by Space Jews with Fancy Ships.
~FIN~
EDIT: Turns out the war lasted longed than I thought, lol.