So when we first step into Halo 4 the setting is laid out pretty clearly. The UNSC is rebuilding and is the dominant but weary and battered victor of the Human-Covenant War. The Covenant is splintered and broken between various factions. A tentative peace exists between the major factions. This contrasts sharply with the Bungie era games where its all about the Human Covenant War. More or less this setting plays out in all the books and through Halo 5.
But this setting 343 introduced, it really doesn’t exist by the end of Halo 5.
If you read Halo Bad Blood it’s very clear that there’s little of the UEG and UNSC left. Earth, Balaho and Sanghelios are occupied. The once resurgent insurrectionist plotters are pushed back into working with the UNSC. The new Covenant is broken. Some of those remanants have even joined the machines.
You have an AI ruling over most of the galaxy with Forerunner war machines whilst the resistance fight from the shadows and their few remaining ships. This is a dramatic change in the setting. You’ve went from a galaxy in which humanity was the dominant power in the galaxy to once again fighting for its existence or at least freedom. The relationship between humans and AI drastically changes. A galaxy which is fragmented between scattered warlords and in flux to monolithic machine empire. A galaxy that’s more or less at peace to one that’s under military occupation and so every world is affected by war and oppression. It’s a pretty dramatic shift. 
TBH Iam still in shock that they went to that much of an extreme. Far beyond Bungies initial idea that Cortana would take over a Halo ring.
Since it’s such a big change, I think it means that 343 will approach Halo Infinite as if it’s a soft reboot of the series. It is a sequel. But in the same sense that Halo 4 was a sequel to Halo 3. The world and the nature of the conflict is totally changed.
We’ll see how long the new setting actually lasts. As it stands, I don’t see the Created lasting too long as the status quo. 343 Industries hasn’t done anything substantial with them development-wise for the last three years, so it’d be easy enough for them to give them their real start and hurrah at the end of Infinite. I’d also question the idea humanity was the “dominant” power prior to Halo 5. Jul 'Mdama’s Covenant was a major threat and rival along with internal strife from the growing New Colonial Alliance. The UNSC had the Infinity, but a single ship a dominating power does not make.
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> We’ll see how long the new setting actually lasts. As it stands, I don’t see the Created lasting too long as the status quo. 343 Industries hasn’t done anything substantial with them development-wise for the last three years, so it’d be easy enough for them to give them their real start and hurrah at the end of Infinite. I’d also question the idea humanity was the “dominant” power prior to Halo 5. Jul 'Mdama’s Covenant was a major threat and rival along with internal strife from the growing New Colonial Alliance. The UNSC had the Infinity, but a single ship a dominating power does not make.
They haven’t done anything substantial with Halo Infinite in general. The game is clearly in very early development with them working on the engine. I think 2020 and they want it to be a launch title for the next Xbox.
They wrote Halo Bad Blood, did some short stories in Halo Fractures, a few comics in that collection they did, Legacy of Onyx segways into post Halo 5 with the implication they will do a future story set in the new setting. Halo Wars 2’s entire plot makes no sense in the old setup. The entire UNSC Home Fleet would have just portalled to the Ark. Then you have the Guardian at the end.
They will likely do a lot more closer to the game dropping. Until then they will do pre Halo 5 to give more creative freedom to authors.
”We are the giants”. Humanity becoming ascendant is a central theme of Halo 4. The Didact isn’t just being paranoid and outrageous when he says this “your ascendency may yet be prevented”. The Infinity and the legion of Spartan 4 points to this. Jul only has a fraction of the strength of the old Covenant. The fact the Infinity could do gunboat diplomacy on the elite home world would be unthinkable and absurd in a Bungie game.
Well they’re in catch 22. Halo Infinite is going to be about Cortana ruling the galaxy, so they have to make it work and use advertising and other methods to sell the idea. Clearly they had hoped Halo 5 would, akin to boiling a lobster, slowly bring people around to the idea. You wouldn’t have sold Halo CE as “lightbulb tries to blow up universe.” Now they have to sell the idea prior to launch, since its impossible to avoid addressing the games central conflict. If they make it work then they would have no reason to can the setting. If that was their aim they wouldn’t be making Infinite at all. I think it’s too major a plot point to be settled in one game and the UNSC would be drastically weakened since all of its fleet seems to have been destroyed.
I’m fine with this new setting but they have to make it very obvious. Make it feel like everybody not with Cortana really is on the run.