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Well, you can, if you and your players don't mind living with the consequences of the adventurers failing completely. A front-row seat for the apocalypse certainly offers some intriguing gaming possibilities.
However, I think it's possible to have all sorts of interesting intrigues and adventures that don't involve epic events.
Bingo.
This is how an "impartial" DM still has bias on the campaign.
Let's pretend a party can only deal with 1 threat at a time. At least based on the idea that there's a finite number of problems they can successfully deal with.
If you want the world to generally maintain a static state, you only throw 1 threat at a time, and keep the coming at a steady pace. The result is, the party will be working on threats, and not advancing on anything else. But "evil" won't be gaining the upper hand.
If you want to overwhelm them, maybe take them down some pegs, you throw in multiple threats at the same time. The party can only deal with one, so the other one "wins". It's really a lose-lose for the party.
The important thing about threats is, as a real threat, the party has no choice to deal with it. If a dragon threatens their lumber business, and they have an opportunity to make a trade alliance in Farville, they don't have a choice. They have to deal with the threat, because if they head out to Farville, the dragon burns down the business they're trying to expand to Farville.
My main point is, you can push the PCs around with threats. Too many, and you change the campaign world to where the PCs are losing, THat's no less true for the plots of NPCs as it is for swarming them with monsters. It is a tool that DM should recognize they posess, and use accordingly.