I am not a master on facebook login issue, but after reading your question, it looks like that if the facebook user is logged in to its facebook account, then it also automatically logs into your application. But you want it to take place at the time when the user clicks on the login button, right.
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.