Running a Long Term Campaign in Fantasy Earth

On Google Plus, Evan Elkins asks

+Anthony Pastores once commented that one of the things that makes homebrew settings better than pre-made ones is a sense that PC action has permanent effects on the setting.  If you make your PC king of +Uz in my game, and I run that setting for a different group either your PC one of his descendants is likely to be the king.

But what about Fantasy Earth?  Two DMs will probably make two totally different Earth's.  For example: if I ran the Roman game I described earlier, it wouldn't look very much like +Zzarchov Kowolski's version of Earth.  But can you achieve that sense of permanence?

If I later use the setting again for new people, wouldn't I have to move time forward to accommodate them?  Won't I eventually bump into a period that isn't the one that interested me in the first place if I did that?

So how do those of you who are running/have run/are planning to run fantasy Earth games handling this stuff?

I been running the Majestic Wilderlands for nearly 30 years since the campaign has progressed from the year 4433 BCCC to  4460 BCCC, 27 years of game time. In general I start the next campaign about two years further in the future from the previous campaign. From what I understand other long term multi-years home campaign settings have a similar slow rate of in-game time versus out-of-game time.

The implication for a Fantasy Earth campaign is that, this is probably something you don't to worry about as even if you play for a couple of decades you are not going to rack up that much in-game time.  Evans mentions a Roman game, he could easily set it during the period of the Five Good Emperors and I would doubt he would would get out of the time period if he started with Nerva in a couple of decades.

However with players who are willing to attempt anything, changes can and do happen. In which case is to treat subsequent history as an alternate history. The nice thing about using an earth based setting is that you have a bunch of ready made "grand plots" in the wings. For example while the period of the Five Good Emperors was the Roman Empire at it's height, the Romans never really solved the succession problem. Leaving the Principate open to anybody with the charisma or wealth to control the legions. All it took for the era to come to an end was for Marcus Aurelius to appoint his son Commodus as his successor instead of finding a truly worthy successor as his immediate predecessors did.

An underlying grand theme of a Roman campaign could easily be about resolving this issue. Successive campaign build up to determine whether the Era of Good Emperors continues or devolves into the warring general that ignited the Crisis of the Third Century. Just about any period of history could be cast with a grand theme based on foreknowledge of subsequent events.

 Note I am not talking about a multi-generational campaign like the Great Pendragon Campaign. That type of campaign deliberately invokes the sweep of history and the characters take multi-year leaps at various time. The players playing the sons and daughters of the original characters. The campaign I refering is the one where the referee simply stick to the same setting when runing a fantasy game. It can cross multiple themes and groups.