i was wondering why nagato become an evil manic bent on world destruction. He use to a nice little kid minding his own business protecting his friends. What changed i think Yahiko his best friend was killed. I think he felt guilty about not being able to protect his friend. And thats when he began his quest to end all Pain in the world cuz of the Pain he got. And also thats why konan follows Pain. I may have some proof in the chapter where jiraiya asked her if nagato and yahiko had died i think she cried , not for nagato but for Yahiko.
I think nagato tried to resurrect yahiko but couldnt bring back his conscience maybe thats when he developed his 6 paths. (+ reps appreciated if u like my theory)