Lanefan
Victoria Rules
Yeah, we're on different sides of the fence on this one.The idea of living breathing game worlds has never really sat well with me even when talking about sandbox play. Where does the world live? How does it breathe? What is is its animating animus? From my perspective thinking off screen is a useful valuable GM technique, but the setting of a game is a designed thing - not something with a life of its own.

Agreed. But note, "the setting is a dynamic place" is just "a living breathing world" writ different.We want players to feel the setting is a dynamic place that changes both based on the decisions they make, but also on its own.
Not quite. The intent is to provide a compelling play space, in knowledge that there will be elements with which the players interact and elements with which they do not.However the intent is to provide a compelling play space with which the players can interact and should be designed with this in mind.
The elements with which the players choose to interact then become the places where they will (almost certainly) cause changes to what otherwise would have happened. Those elements that are left alone, however, will just proceed on their merry way as pre-determined by the DM; with later knock-on effects (if any) to the players/PCs being determined via cause and effect as play rolls on.
Using my example from earlier regarding the fall of the West Marches; an obvious knock-on effect to the PCs would arise had their next intended mission been in the Jasper Mountains, as that has now just unexpectedly become a war zone. But just as easily that war in the west might have no effect on the PCs at all other than to provide conversation fodder in the taverns. Relating the news, however, adds to the sense that things of potential importance are also happening in places other than where the PCs happen to be - that the world extends beyond the PCs' field of view or perception.
Put another way, it's a living breathing setting and you-as-DM are its beating heart.I do not design worlds. Depending on the game I might design settings. I might design adventures. I might design scenarios. I might frame scenes. I might make GM moves. I might design sandboxes. In every case I am designing a space to be played in where players can make decisions that matter. Those changes to the setting that occur between sessions, especially the ones that happen off screen are the result of deliberate design. I am the animating force and bear a responsibility for that design work.
Adventures, scenarios, framed scenes, a sandbox - all those are just bigger or smaller parts of the whole (sometimes even parts of each other e.g. a scene is part of an adventure which in turn is part of a sandbox).