It’s simple, yet it brims with complex issues.

“The Wall” is one incredible war movie that utilizes a handful of characters to make a statement about what motivates soldiers to fight and what motivates countries to go to war. Because it’s set mostly in a small area, it’s more like watching a play than watching a movie unfold.

Besides, wrestler John Cena has a secondary role. He’s been hitting the big screen as an actor in comedies, much to my delight (watch his turn in “Trainwreck” if you haven’t already seen it.) Now he takes a dramatic turn as Sgt. Matthews, one of two soldiers serving in what is supposed to be the last part of the Iraq War in 2007. Sgt. Isaac (Aaron Taylor-Johnson, “Nocturnal Animals”) and Matthews are trying to figure out what killed eight contractors who were working on a pipeline in the desert. Both are pretty sure the killer has left the scene .. that is, until a rain of bullets begins again, and Matthews is shot.

Eventually, Isaac, too, is wounded. And he begins to talk with someone on the radio — someone who may not be exactly who he seems to be. Isaac begins a verbal cat-and-mouse game with him. 

Screenwriter Dwain Worrell has a knack for believable, expository dialogue. Director Doug Liman (“Edge of Tomorrow” and “The Bourne Identity”) keeps things interesting by showing us, over and over again, Isaac’s perspective. He also doesn’t clutter up the proceedings with a soundtrack or score that you’d expect from most war-based films. This increases the tension 10-fold.

You’ll find yourself on the edge of your seat within the first 15 minutes. The screenplay is smart, because it focuses on so few characters. Johnson is terrific as Isaac, around whom the events revolve. He’s desperate, possibly dying, and we can almost read his mind as he reacts to his situation.

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This may look like an action movie at first glimpse, and there are a few minutes of action within it. But even though it’s a war film, it’s not really an action flick. Rather, it’s a character study, mostly of Isaac, a kind of thriller, you could say, about an ordinary man trapped in extreme circumstances. It’s a movie that invites — in fact, nearly requires — viewers to mentally place themselves in the plight of the main character. You’ll be asking yourself “What would I do in this predicament?”

The finale will continue to make you think long after you leave the theater. This movie, like other good works of fiction, contains a lot of unsettling truths.