I agree. Though without a central authority like the UEG to guide things along a general path, human colonies would be much more splintered and differences in levels of technology would have fueled additional colonial wars.

:As far as government, I imagine 2,3 or more factions would have
: gained popularity, colonizing worlds and spreading their reach. This would
: have likely lead to more human wars, it is in our nature. If the Covenant
: threat would have united these factions is an interesting question.

Well, the question is, how long would the inevitable unification of human military forces have taken? It's roughly 400 years from 2170 to 2525, so I suppose there would have been more than enough time for potentially a Second Interplanetary War to break out and for the UNSC to win that one. However, if the victorious communist/fascist factions of the First Interplanetary War managed to already expand their colonies considerably, it would have been much harder for a demoralized UNSC to defeat them.

In any case, in a scenario where the UNSC didn't win the Interplanetary War, it will pretty much assuredly be more difficult for humanity to defeat the Covenant in 2552, or we could lose entirely.

Although it's pretty much impossible for the UNSC to lose the Interplanetary War. It had the support of the UN, the USA, presumably the UK and France as well -- the whole international community.

It's too bad this period isn't fleshed out a bit more. For instance, I'd like to know if the communist factions had the support of China or any other modern communist country. But I suppose this is being left out intentionally for the franchise to not get too political.