“Emperor” opens Friday at Sundance Cinemas; PG-13, 1:45, three stars out of four.

“Emperor” is a war movie with no war in it (well, barely — got to have something to put in the trailer.) In fact, it’s a movie about the uneasy peace that occurs right after the cessation of hostilities, when one side has surrendered, and yesterday’s combatants becomes . . . what, exactly? Equals? Occupied and occupiers? Liberators and the liberated?

In this case, the war is World War II. Japan has just surrendered to the Americans, and Gen. Douglas MacArthur (Tommy Lee Jones, and is that ever great casting) strides the ruins of Tokyo like a Colossus. Having been responsible for the devastation all around, the Americans have to shift into a postwar occupation phase. They have to punish the guilty, but help the innocent rebuild. It’s not an easy distinction, not an easy task.

Chief among them is the prosecution of war criminals, and in particular whether Emperor Hirohito should be charged, particularly with ordering the attack on Pearl Harbor. MacArthur is in a dicey spot; politicians in Washington want vengeance over their former enemies. But MacArthur also needs the peaceful occupation of Japan to succeed, and if he hauls a leader that the Japanese people consider a god before a tribunal, that will be awfully difficult. Jones plays MacArthur as a cagey man with presidential ambitions, but with a humane side that might trump those aspirations.

So he tasks Gen. Sellers (Matthew Fox of “Lost”) with finding out the truth. Much of “Emperor” plays like a dry procedural, as the stifffly formal Sellers interviews higher-ups in the Japanese command, trying to ascertain what people knew and when they knew it. He finds Japanese culture to be a confounding one — the most modern of all Asian nations, yet with traditions and a mindset that stretches back 2,000 years. “If you understand devotion, then you will understand Japan,” he is told.

But Sellers is undertaking another investigation as well. His Japanese girlfriend (Eriko Hatsune) was left behind before the war started, and he’s trying to find out what happened to her. On their own, each of the investigations might be too slender to sustain a movie, but screenwriter Vera Blasi and director Peter Webber (“The Girl With a Pearl Earring”) successfully blend the political with the personal. At first, I thought Fox was playing Sellers as too stiff to be the film’s lead, but by jumping back and forth between the storylines, we see that’s his public self. His private self is more gentle, more wounded, and the deeper I got into the movie the more drawn in I was.

Fox’s internal performance makes a nice complement to Jones’ outsized MacArthur (corncob pipe and all), and although we want to see more of Jones, Webber uses him efficiently and effectively throughout the film. The film ends with a spot-on recreation of MacArthur’s actual meeting with Hirohito, who proves to be charming and decidedly ungodlike. (For the reverse view, check out Aleksandr Sokurov’s 2005 film “The Sun,” which tells the same events from Hirohito’s perspective.)

Overall, “Emperor” isn’t much of a mystery or a war movie. But it is a sober and affecting meditation on the lasting effects on war, with an understated but still-relevant message that America may reveal its best self not in its moment of military victory, but in the moments that happen afterward.