Revolution
Discoveries and wars that led to disappearance of religion.
It started when someone discovered the Flying island and established a settlement there. Multiple events followed and led to the fall of all religions: The proof of physical existence of Angels, exploration of their land, their testimony on non-existence of one true god, discovery of Hell entrance, establishing Devils as a humanoid race and more. All of that shook the foundations of most religions which led to the followers abandoning their faith and thus disbanding the religion or in some cases religious wars that attempted to make people believe with force, but ultimately failed.