What's the rule here, three outbound links to one domain is too many, and gets a hub called?

Depends on how you go about it. Generally, two outbound links per article. However, if you divide a book into one chapter per hub, you can add a link to the each hub for that site...still, two outbound links per site.

Hubpages wants to keep readers in the Hub which makes sense in a way.

Generally you should aim for no more than two.

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.