Unfortunately random strangers like myself don't have any more insight into his life than you do. After all, you know the guy. We only know about him from the paragraph of text you provided.
Bearing in mind that I can only guess what's going on in his life, it may be that your ex-boyfriend is going through a transition in his life. Some people "discover" (or "re-discover") God as young adults, after experiencing a rough patch in life, the death of a close friend or family member, or just an existential crisis in which they spend a lot of time thinking about the big questions like we why exist and what the meaning of life is. Perhaps the emptiness he felt after you were no longer in his life caused him to try to fill that void with God/religion instead.
When people convert to a new religion, or "re-discover" the religion in which they were raised, they sometimes become very zealous and passionate about it, at least for a while, because it seems so fresh and exciting to them. This "convert zeal" may be responsible for your ex-boyfriend deleting his social media accounts, so that he can instead focus on his new religious passion. Anyways, if that's what your ex-boyfriend wants to do with his life, he is free to do it.
You've already broken up, so you are also free to move on too.
Maybe he is going to turn to God, like go to church on Sundays and preach. Just move on from him. Let him live his life.
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.