I think the most crucial thing to ending violence is education. In the future, the most important things education needs to teach (aside from maths&english) are history and philosophy (esp. ethics). Learning history prevents us from repeating mistakes, and philosophy teaches us how to think and live a meaningful life. The study of religions should also be a major part of these courses - not just one religion, but all religions as a whole.
So if everyone were atheistic that would be progress, but I think religion is merely a primitive philosophy, and what we really need to do is get people thinking more about philosophy in general. There are many ways to be ignorant.
Also, if everyone were catholic, then conflict would be inevitable and eventually catholicism would splinter into many sub-religions. Eventually some new prophet will come along and start a new religion, and we will have come full circle.