Why Are Batman And Superman Fighting In BATMAN V SUPERMAN?

It's a year from the release of the film. Here's a tidbit to tide you over.

We're a year out from the release of Batman v Superman: Dawn of Justiceand to celebrate - and to get people theorizing and guessing and wondering - I wanted to share a tidbit about the movie, and about why it's a 'versus' film in the first place.

We know that Batman and Superman will fight - it's right there in the title! - but why? What would cause these two titans of heroism to tussle? Well, an outside force, of course.

Spoilers follow. 

In Frank Miller's seminal The Dark Knight Returns Batman and Superman duke it out when the president sends Supes, a lackey of the government, in to stop Batman as he cleans up the streets of Gotham and effectively takes over the city. Superman tries to reason with Batman, ut Bats going in for the kill, and a fight ensues - one where Kryptonite and an exo-skeleton give Batman an advantage. 

In Batman v Superman Superman is no lackey of the government; if anything many of the world's governments distrust the guy. But it is Superman who goes to Gotham and starts the confrontation... at the behest of Lex Luthor. And unlike The Dark Knight Returns, Superman comes out swinging, pulverizing the Batmobile with one punch. Why would Superman do Lex Luthor's bidding? What is Lex hoping to accomplish? That would be spoiling. But know that when the fight is over, Batman will be able to point to Superman and say, "He started it!"

currently the actual title, but we'll see.