That's an absurd belief. Only a child (and a particularly ignorant one) could seriously believe something like that.
Depends on what you mean by "seen". I you mean believe that things you can't see with your naked senses, like microbes, radioactive decay, and subatomic particles don't exist, than I'd say you are a fool. If you mean believe that things you can't measure using instruments that enhance your senses, like microscopes, geiger counters, and neutrino detectors don't exist, than I'd say you are a realist.
Of course, your entire "question" is one of the standard dishonest theist "gotchas", where you follow up with "well, if you can believe in things you can't see, why don't you believe in god?" So I'll answer that one for you to. Evidence.
There is evidence that things we can't see - like germs and neutrinos - exist. There is no evidence gods exist.
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.