: 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.

I wouldn't go so far as that. The worse the Friedenists and Koslovics I imagine could have inflicted on the UEG is a simple defeat. Pack up your gear and ship it back home. No resounding defeat and blow to their economic and military capability. As I mentioned in my first post, it would likely just infuriate Earth's powers to overwhelm them as soon as possible so it never has to deal with foreign border disputes in its journey out into the universe.

: 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.

Pretty much, yeah.

: 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.

Communism never seems like a guaranteed unifying factor with the People's Republic of China. Keep in mind that they had often clashed with the Soviet Union and Vietnam both politically and violently.