Spoiler alert: Saddam Hussein didn’t have weapons of mass destruction. George W. Bush and his buddies made all that up, fabricated intelligence and used it to sell the war they were hellbent on waging. The thousands of Americans killed in Iraq since the invasion were put in harm’s way under false pretenses.

Oh, you already knew that? I would have thought so, but for some reason Green Zone director Paul Greengrass seems to be under the impression his new film drops a bombshell. Sure, it was made two years ago, but even then this would have been old news. Intended as a thriller with brains, this is perhaps the most unnecessary message movie ever made.

Greengrass, of course, has given us notable films over the years, from the fact-based dramas Bloody Sunday and United 93 to bristling paranoid fantasies like The Bourne Supremacy and The Bourne Ultimatum. I think it’s safe to say that, with Green Zone, he was attempting a hybrid of these two genres. I think that because he’s said so: “I wanted it to be ... a movie that would hopefully take some of the huge audience that had enjoyed the Bourne series to a real-world setting and encourage them to consider whether the mistrust and paranoia that characterized Bourne’s world was so farfetched after all.”

Hence the casting of Matt Damon as U.S. Army Chief Warrant Officer Roy Miller. Set in Baghdad during the early days of the U.S.-led occupation, the picture mixes fiction with thinly veiled fact. Between missions in the course of which Miller’s unit again and again fails to turn up WMDs where Pentagon intelligence says they should be, Greengrass introduces us to stand-ins for several of the debacle’s key players.

There’s an Ahmed Chalabi type (Raad Rawi) waiting to be back-doored into power by the coalition, and a faux L. Paul Bremer (Greg Kinnear), a lethally smug administration lackey with zero patience for anyone who second-guesses White House wisdom. Amy Ryan plays a journalist clearly modeled on disgraced Times reporter Judith Miller. Igal Naor costars as General Al Rawi, a senior Iraqi who’s a composite of all those former insiders whose faces ended up on playing cards when they might have proved helpful in holding the country together.

One day, a local (Khalid Abdalla) approaches Miller’s outfit and offers to take it to a secret location where the general and some high-powered cohorts are meeting. The soldier figures if he can’t find any WMDs, he might as well snag a few VIPs, so he decides to go rogue. At this point, the story pretty much leaves military reality behind and forges, guns blazing, into action-thriller territory, though it never comes close to achieving the crazy-cam exhilaration of the Bourne pictures.

What it does achieve is a sort of Operation Iraqi Freedom for Dummies. Greengrass seems to assume moviegoers haven’t picked up a paper, checked out documentaries like Charles Ferguson’s No End in Sight or read any of the dozens of bestsellers on the subject, so he offers up a preachy point-by-point recap of what went wrong and why America never should have gone to war. The problem isn’t just that the filmmaker doesn’t tell us anything we don’t already know, but that history lessons and sanctimonious speeches don’t lend themselves particularly well to the action-thriller form.

Sorry to say, this is not Greengrass’ finest hour and 55 minutes. Or Damon’s, Kinnear’s or Oscar-winning screenwriter Brian Helgeland’s. A lot of major artists have made movies about this war, and I’ve found it baffling when they’re met with indifference. Should that fate await Green Zone, it will be far easier to understand.