In ways both big and small, “The Wind That Shakes the Barley” is a rebellion movie less interested in the battlefields of the Irish Civil War of 1919 than in the psychic struggles that accompany a nation’s uprising; or to borrow from its title, this Ken Loach epic is less about the swirling winds of unrest than how these gusts push a landscape in unexpected directions.

It is a theme most vividly realized on the rolling Irish countryside, as one accidental fighter suddenly realizes he must kill a boy he knows —a boy who knows him — because the latter divulged secret information to the enemy. It’s an essential act of strategic retaliation, but as the man holding the gun paces and frets, agonizes and shoots, it becomes clear that he has dived headfirst into a well of violence that goes far deeper than he imagined.

Damien O’Donovan (Cillian Murphy) never wanted to be the man holding the gun. Dragged into a conflict he fought so hard to avoid and brought to the realization that no military victory will fully heal his country’s wounds, he is Ireland’s everyman. He’s also one of millions; where movies about the battle for independence typically tell tales of smaller armies finding ways to outmaneuver and outgun their oppressors, Mr. Loach’s version is more interested in the way an uprising can turn a society on itself, destroying the fabric of a nation, a neighborhood, and a family.

A young doctor with plans to leave Ireland for a tenure at a London hospital, Damien’s sense of peace is shattered quickly. It is during a farewell visit to Peggy’s (Mary O’Riordan) farm that a gang of Black & Tans, or British peacekeeping forces, invade with guns drawn and force a half-dozen men up against a barn. They inform the group that all public meetings — including sporting events — are henceforth banned, and as they antagonize the natives, demanding their names in English, they drag Peggy’s non-English speaking grandson (Laurence Barry) inside and beat him without mercy.

The vicious encounter is all the evidence Damien needs to cancel his venture abroad and put his life on the line to defend home and family. It’s a decision that immediately brings him closer to his brother, Teddy (Pádraic Delaney), an activist leader who’s delighted with Damien’s decision to enlist in the Irish Republican Army. As the two train with their countrymen in the hills, steal weapons from the police, organize attacks in hopes of causing the most possible damage, and find within themselves the strength to one day walk into a pub and ambush a gathering of British troops, they discover that guerrilla warfare is not as simple as they imagined.

Nor is keeping the peace. As the Anglo-Irish Peace Agreement is announced — the resolution that formed the Irish Free State as an independent domain within the British Empire — the brothers find themselves at odds, one embracing the treaty as a victory and the other decrying it as yet another insult.

There’s a lot of talking in “Wind That Shakes the Barley” — the same brand of unrushed, unfiltered, hyperrealistic talking that has become a staple of Mr. Loach’s distinctive style. But what’s interesting here is the way the words, which can admittedly grow dense at times, serve as a counterpoint to the action. While there is something definitive to the events on the battlefield — something concrete about these bullets, bayonets, and this blood — there is also something far more ambiguous and uncertain about the debates that follow, which question the nature of victory, loyalty, and heroism.

It’s in the involving eyes of the tortured Mr. Murphy that the movie finds its longevity. From the days of peace to the unlikely battlefields (captured with remarkable beauty by the director of photography, Barry Ackroyd, who makes great use of natural light), it’s his evolution from spectator to revolutionary to extremist that helps these later, more verbose scenes resonate. For while revolutions begin with blood, they usually endure thanks to public consensus — as violence ultimately gives way to a war of words.

And it’s in the sound of that meeting of the minds — not the clashing of the swords — that one can hear the birth pangs of a new republic.

Opens March 16 (323 Sixth Avenue at West 3rd Street, 212-924-7771).