"Why did America go to war in Iraq in the first place?" Paul Greengrass' Green Zone asks that very inconvenient question and the result is that the general public probably won't go. It's not Bourne 4, as people joke, and it's not non-stop action. It's handled masterfully in the way you'd expect from a pro like Greengrass. In the end you will find it a sharp, smart and very effective conspiracy action thriller.

Miller (Matt Damon) is the leader of a group of soldiers tracking down those elusive weapons of mass destruction. The "very good intelligence" he's given as to their locations leads to endless military confrontations, but doesn't produce any weapons. As everyone knows, the claims by the administration were built on speculative lies and unchecked rumors. Miller finds himself a pawn in a tug of war between an old CIA hand (Brendan Gleeson), who is trying to deal with the actual facts on the ground, and Poundstone (Greg Kinnear), the chief American official in Baghdad, who is only interested in information that fits the administration's pre-supposed notions. There's also a reporter (Amy Ryan) who has been dutifully repeating the official line in her news reports thinking she's getting the inside track. The rival American factions are after the one Iraqi who could reveal the truth. The CIA sends Miller to bring him in, while Poundstone wants him taken out... for good.

Damon is as enjoyable to watch as he always is. He's likable and always believable. He makes you feel the danger Miller is in. He comes off as if he's in actual peril. Plenty of actors are incapable of achieving that, Damon is uncanny in this respect. It also helps that he's supported by an array of some of the best working actors today: Ryan, Kinnear and Gleeson rounding out the cast.

If you don't pay attention to every minute, you'll most likely miss a thing. If you actually pay attention, you'll be greatly rewarded. It moves along at an extremely brisk pace and, for the most part, everything feels fleshed out. The last half-hour is as suspenseful as it is dizzying as director Greengrass uses his raw gritty cinema v?rit? camerawork with QueasyCam style to put us in the midst of the action. It's intense and raw, similar to the overall tone of the film. Not many directors can pull off that rush of sensation.

While the story takes liberties with the drama, the basic facts are not in dispute: the Weapons Mass Destruction our reason for starting the invasion in the first place are not there and the administration know that for a fact. The film is based on the non-fiction book "Imperial Life In The Emerald City" by Rajiv Chandrasekaran for those who prefer the facts without the shaky camerawork.

Green Zone is a film that offers an important look back at the war's start. That makes it important, no matter how much people on both sides of the debate might prefer to talk about something else. It's difficult not to embrace Green Zone for its greater ambitions, the terrific performances, the chaotic style, and certainly, the wonderful tension and action.