By now, you've probably heard that Robert Downey Jr. is about to sign on to appear in Captain America 3, which will borrow its storyline from Marvel's Civil War mega-event series that was published back in 2006. Or possibly, Cap 3 could be the trigger for the Civil War storyline, which might take place in Avengers 3, instead. The news reports are a bit fuzzy on that detail.

Regardless, Civil War is coming to the big screen. So what is it, and why is it still considered such an important storyline? Civil War tapped into the real-world zeitgeist of fear over civil liberties and homeland security in a post-9/11 world.

Basically, it's like this: A young superhero team engages in a foolhardy attempt to take down a powerful villain in the 'burbs. Predictably, it all goes horribly wrong, and an explosion kills 600 people, including an elementary school and all of the children there. Public outrage at the heroes' irresponsible actions causes Congress to pass a "Superhero Registration Act," a bill requiring all superpowered people to reveal their secret identities to the American government and agree to work for Uncle Sam.

Iron Man decides to support the Act and tries to bring other superheroes around to see the logic in it, but it doesn't sit well with Captain America and many others. Hence, a civil war begins. And, well... it gets ugly.

What makes Civil War unique, is that unlike other comic book "wars" where Earth or the entire universe is at stake, the characters in this story are fighting over ideology. One side believes that the responsible thing to do is to make themselves accountable to the government, in order to prevent another genocidal disaster. The other side believes that giving up their secret identities and allowing themselves to take orders from the government is a violation of basic freedoms, akin to the Patriot Act.

In the film Captain America: The Winter Soldier, Steve Rogers came to see the operations of S.H.I.E.L.D. as a serious threat to human freedom. So this train of thought is already planted in his mind. Civil War makes perfect sense as the logical next step to up that ante.

Of course, many elements of the story will have to be condensed or excised altogether to accommodate a two-hour movie. For example, the comic book used a huge cast of characters from all over the Marvel universe, and obviously a movie can't dive that deep. But the crux of the story hinged on these two viewpoints embodied by Iron Man and Captain America, and with Downey appearing in Cap's next movie, it sounds like the pieces are falling into place.

Also, it's well known that Chris Evans and Robert Downey Jr. (and probably Chris Hemsworth, too) are only contracted up through Avengers 3, and Evans has made it clear he intends to be done after that. Downey's future is a little less certain. Yet Marvel has said it has a plan in place to keep its "cinematic universe" chugging along until 2020 and beyond. Civil War could give Marvel a clean solution for continuing the Avengers franchise without its two biggest characters.

One other thing...

Remember that news story about Sony cozying up with Marvel with the notion of letting Marvel use Andrew Garfield's Spider-Man in Marvel's movies? It's worth noting that Spider-Man played an extremely pivotal role in the Civil War storyline.

Hmm.