The app store doesn't detect that you have Xcode installed, it detects that you have the Xcode installer installed. That must still be around somewhere.
Uninstall XCode 4: How to fully remove Xcode 4.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.