B/X Known World
Like a lot of others, I've found that the players only care about the world if/when it directly matters to them in the moment. Tell them there's an order of battle mages and they'll yawn. Throw a squad of battle mages at them and suddenly they care. If you use the distinction between foreground and background, the players (and their PCs) generally only care about what's in the foreground. The background is irrelevant...right up until you bring it to the foreground. Another way to say it is unless it directly matters to the story at hand, it doesn't matter.