Given that I know nothing about your code, I'm confused why you have Camera within Display. While logically a display is displayed with a camera I would think your object structure, if you are making them interdependent would be inverted. Cameras use displays to show their field of view Your binding of a camera to a display may also seems to negate the ability to have multiple monitor support. This is all just reading logically and trying to rationalize how your objects interrelate so take this with a grain of salt but you may definitely want to re-examine why you have those objects linked the way you do.
Well, as I said above, Display is a subsystem, rather than a display in the sense that you seem to interpret the name, which is understandable. It owns the Window object, the Renderer object, handles creation of the dialog boxes. It owned the camera object largely because I needed to put the camera somewhere. I've put the camera in the World class, as owl mentioned that he did, and it does simplify a lot of code. I had to do a bit of fudgery since the Menu is essentially another World object, and also needed the camera. But I just realized that I could probably have a static camera in the base class....
I considered including multiple monitor support, but I don't have multiple monitors Also, I don't think this would work well split across multiple screens: