If you want the Server to be able to Contact the client when it wants, then whenever the server get the client Socket object using the accept() method, store it in a HashMap or ArrayList depending on your necessity. So now you have the client socket object saved with the server.
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.