First thing's first, he shouldn't have repeated the style of Dogville. It worked there, yes, but it isn't something that was going to work twice. It weakens this film quite a bit, because it all feels like a been-there-done-that. I'm not 100% sure what von Trier's point is supposed to be, but the film seems to be trying at both a commentary on American racial attitudes as well as an allegory of the Iraq War. The latter part mostly works, although even it has some flaws. Grace (played now by Bryce Dallas Howard), unlike the United States, doesn't have to use force to free the slaves of Manderlay. There is no collateral damage, and it's hard to dislike Grace for wanting to help these people. However, it does make a good point that helping these people form their own society has its own dangers. When all they've ever known is servitude and cruelty, how are they going to treat their fellow man? That argument may be condescending to the Iraqis, but I have to admit I agree. As far as the racial themes go, Lars von Trier, a man, I don't have to remind you, who has never even set foot in America, has no idea what he is talking about. Well, I suppose some idea. I mean, everybody reads. But the American racial situation is far more complex than he understands, and the film, with regards to this theme, echoes the kind of jackassery of Neil Young's "Southern Man". It's not surprising that von Trier's indictment of American society doesn't work; it didn't work in Dogville, either. He even ends this film exactly the same way, with David Bowie's "Young American" playing over a montage of supposedly damning photos. The final photo is of a black man cleaning off the statue of Abraham Lincoln in the Lincoln Memorial. The irony of just how non-damning that image is is lost on Lars von Trier.
