I want to correct you people on one thing. You have argued that composite civ has psionic resistance, and that could allow them to resist neutron sweep colossus strike. Well that isn't the case. Firstly, their psionic protection is far from invincible, and secondly, neutron sweep has nothing to do with psionics. It bathes the planet in a wave of neutron radiation. Somehow it kills only sentient beings with developed nervous system. Although the colossus is pretty faulty, taking a long time to charge up, it is unlikely that composite civ can destroy it. Whilst they have a warfleet in space as shown by a spinoff game Sid Meier's Starships, it is laughably small and visibly quite weak in comparison to what Stellaris nations often dish out. Result of this matchup depends solely on the tech level we take both contenders at. In the original post it is said that UNE is taken at their late game appearance, which means they can deploy some crazy stuff, considering all the options, technology, ascension perks and enemies they often take down. As for the composite civ, then if they are taken at the height of their Beyond Earth canon, they can put up a pretty good fight, and they get a space fleet, but the technology isn't as crazy and they do lose to UNE. If they are taken at the Alpha Centauri canon peak, they do not get a starfleet, but their tech gets better. However, because in such case composite civ has access only to some limited orbital combat assets (propably), even if UNE cannot take them on ground (we have no way to determine that, since Stellaris ground combat is pretty nonexistent, and armies are defined only by some loose descriptions and a bunch of tech modifiers), they can just park their fleet in orbit and keep slamming warheads into the enemy, or destroy the battlefield with their colossus weapon, whichever one is currently equipped. Its hard to see composite civ coming out on top, or even getting a draw out of that. But I am not that lectured on the subject of Alpha Centauri technology, I have only read up a little, so I may miss something.