With so many different campaign settings in print, it’s likely that, for most people, the setting in a game comes before character development. The benefit of this, is that players can read up on the setting and learn about it, extracting any amount of information they want from the campaign world. Though, you might want to limit them to certain sections of the book to prevent meta-gaming
Alternatively, you can have players build their characters first, and design the world around them. In this scenario, the GM can attempt to extract the campaign world from the characters backstories, building out from what they’ve already created.
Do you create your campaign world first, and have your players design their characters in the world? Or do you have your players design their characters, and then design the world around them? Or is it a mixture of both? Let us know!
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Setting always first…actually System first. Many systems come with a default setting and it would be difficult to diverge from the setting. Shadowrun, Ars Magica, etc. My group first chooses a system or genre (“We are tired of science fiction and want to play fantasy next.”). Often this means a default setting.
If the next game is using a broad genre (such as fantasy) or a system with much support (such as D&D) then I would assume it would be possible to select a setting after character generation. However, often a specific setting will include character options based solely on the setting (new abilities dependent on a class unique to the setting or bonuses based on what region of the setting the character is from).
Setting gives direction and focus to character generation. One player making a steam-punkish character and another making a tribal barbarian would make for a difficult selection of setting if setting was chosen after the fact. As a DM I want the players to buy into the setting, since that will be the focus of interaction as we play, and to do that they need to understand the setting and how it relates to their characters.
Setting first.