Lib/validators seems by far the cleanest. However you may need to load them in before your models, so probably from an initializer.
If you place your custom validators in app/validators they will be automatically loaded without needing to alter your config/application. Rb file.
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.