With the latest comments from Paul McCartney on the reason the Beatles broke up, I thought I'd pull out my high school research paper on that very topic. From May, 1976. If any one is interested, here is the link to a copy of the paper in PDF form:
https://drive.google.com/open?id=0Bxy3l1nvun7iOXNVcG1UOFc4cEE
The more you are prepared, the less you need it.