Requesting user input from outside the GUI code, do I need Events or Action to communicate with the GUI in this case?

It should be possible for your background thread to spawn a dialog with invokeAndWait().

The publisher will have a public add/remove listener, where the subscriber will add itself or be added via another channel to the EventListenerList in the publisher.

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.