You need to keep track of which overlays you created in an array and if you need to close some of them you can find them in the array and setMap(null) on them or another method that gets rid of them (close() in the example below). It is useful to create a custom id for your markers or overlays in your array so you can quickly locate them.
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.