You can't "force" a value that violates a foreign key. That's the whole point of foreign keys.
Do not use a dummy value such as zero to indicate a nonexistent value. There are only two correct ways to deal with an optional association. The first is to use nulls to indicate no association in a given instance.
The second is to rework your schema so as to conform to sixth normal form.
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.