Jon Negroni has unveiled a colossal new theory that will completely blow your mind. He has created a unified theory of Pixar films that asserts that all Pixar films are part of one vast narrative, a tale of the ultimate dethroning of humanity by animals and machines. His entire theory can be found here, and it is worth reading. If you just want to know the basics, this timeline explains everything:
There ya go. Take this knowledge, and share it with the world.
-Earnest (follow me on twitter @earnestp)