Player choices affecting a massive online world

What you could do is have certain quests that involve many people or require a certain number of people to complete it in order for something to happen. You could also have a counter-quest/decision that prevents it from happening (or causes something different).

Then, once the requirement has been met, you can change the world based on that for everyone. Then, you can just keep going with that storyline and add new quests based on it and make it part of the history of your world.

I know that some games do things like this but have "ages" or "epochs" whereby after say, one year, they reset the server and everything goes back to level one and the "world decisions" that were made are undone. Thus allowing people to make new decisions and see how they affect the world.

You could even make the trigger for the reset a huge end-game quest that involves all the players on the server. So that, unlike many MMOs, you can actually beat the game!

Edit

To address Lohoris's concerns (see comments), you could set up a system where the story for one "age" ends but a new story begins based on the world at that point. So if a city has been burned down because of a collection of player decisions, that city stays burned down, but maybe some pirates and bandits have moved into the ruins. Perhaps two ages later the players have the chance to rebuild the city. There's a lot you can do here.

Doing it this way, you give players the ability to control how the world and the game itself evolves. Which would increase the immersion factor immensely in my opinion.

I bet you want to have a look at A tale in the desert, and see what they did there.

Another idea could be thinking about it as something like Minecraft.

That would be a pretty peculiar world — one in which you are affected by your own decisions, but not (presumably with the exception of direct player–player interaction) by the decisions of anyone else.

Also, as you note, the world would get fragmented pretty quickly. Even with just a couple of dozen possible yes/no decisions, there would enough total combinations that pretty much each of your players would quickly end up in their own world shared by nobody else.

Some of the ways in which this might perhaps be made to work include:

• Severely limit the number of choices that trigger fragmentation, maybe only to one or two really big issues (like "start global nuclear war" vs. "don't start global nuclear war").

• Keep the fragmentation localized. So players who burned down the village and players who didn't would stay in the same world except when they enter the village. This might feel pretty weird — if you walk into the village with another player who didn't share your version of it, would they just disappear? — but then again, the whole concept is pretty weird to begin with.

• Allow player interaction between the instances, either on a meta-game level (e.g. through in-game chat channels) and/or directly in the game (e.g. by showing players in alternate instances as "ghosts" that can interact to a limited extent). The latter might work reasonably well with the "local realities" idea above.

All in all, this seems like a rather strange way to design a game, at least if taken at face value, and I suspect that "allowing more social interaction among players" is far from the only problem you'd face in trying to implement something like it. That said, I'd certainly like to see someone try this, if only for the weirdness factor.

It doesn't need to require too many instances. If you fragment the world into specific areas where choices are made (like that village being one fragment with a destroy/save choice) then you only have to make separate instances for that particular area. So you have a world fragmented into maybe 100 or so cells, where there are anywhere from 1 to 8 different instances for each are (0 choices to 3 choices). Plus if you get clever about the choices (such as not destroying the village out of mercy, and forcing the villagers to pay you to save the village) you could actually have more choices than instances. The biggest problem with this mode is that each area would have to load independently from one another; it would be kind of difficult to do a free-roaming MMO this way.

Recently, I've been thinking of way how to implement persistent world into MMO game. World where many players together would choose how to influence world and how to shape it. Of course that lesser changes would require less players with less power (influence). But to implement something like this in truly persistent world it would take immense amount of time and coders.

One way to bypass this problem is to make world reset after certain amount of time. This however is not taken enthusiastically by typical MMO players. They like to build their character. They want to build their power, to amass it. Server reset would upset pretty much all of them.

There is however one way how to let keep at least some if not all of their power regarding influencing world. My solution is to let them, right at the start, to create their own clan or lineage. Their character is then champion from their lineage and is representing it. Anything they do will either benefit or hinder their lineage. Well mostly benefit as we're talking about sort of building experience. And when server reset come and when there will be new age, players will simply choose new champion (create new character) from their lineage. They'll keep all their amassed influence and possibly more benefits (epic items, buildings generating money, rights...)

And that's basically it. I think this way will be both builders and explorers more or less satisfied. Of course we can't tell unless we try it, but it's sound good as concept to me.