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!