No, you don't have to sign up for all of them however it is always a good idea to have as many revenue sources as possible in order to maximize your earnings potential.
The answer is no, you don't have to do all of them. If fact, you don't have to do any of them! Google isn't affiliated with Amazon nor eBay as a prerequisite to sign up for 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.