Ken Loach speaking at the Cannes film festival said The Wind That Shakes The Barley was a story he had to tell.
By Darren Waters
BBC News entertainment reporter
Set in Ireland in the 1920s it recounts events that led to the formation of an independent Ireland and the creation of Northern Ireland.
Loach's aim is to cast his political eye on events that are rarely discussed in the UK and beyond and remain open wounds for many Irish citizens.
The Wind That Shakes The Barley is set in 1920s Ireland
Cillian Murphy plays Damien, a young man set to leave Ireland and become a doctor in London.
But events overtake him.
At the start of the film, Ireland remains an effective colony of the UK; with British soldiers stationed in the country.
Damien witnesses the murder of a young friend, killed at the hands of brutal British soldiers because he would only give his name in Gaelic, and not in English.
As he prepares to depart for London, soldiers attack a train driver because they have been told by unions not to carry British military personnel.
Encouraged by friends to fight the British he enlists in a small cell of Irish republicans, part of the IRA.
Paul Laverty's script is one-eyed, and unashamedly so. Loach and Laverty's aim is determinedly political - to show an occupied country which rises up to throw off the yoke of an invading army.
It is a clear attempt to find resonance with events in Iraq, with the US in the role of the Empire clinging on to the past.
Such lack of balance, however, results in a one-dimensional script. The British are depicted as cardboard cut-out thugs and the motivation for the protagonists is delivered with a heavy hand when a lighter touch is needed.
The film works best when examining the emotional turbulence felt by ordinary Irish men and women when they have to turn to armed struggle and murder.
In one scene the Irish Republican Army attacks a British troop convoy and many of the Republicans are visibly distressed with the deaths they have caused.
But the power of the scene evaporates when the soldiers return home only to find British troops attacking an Irish farm and its female-only habitants as part of a search for IRA members.
It clumsily absolves the characters of any guilt over their murderous actions and sets the tone for the subjective stance of the film.
The film heralded Ken Loach's first Palme d'Or win
Murphy handles his role well - and wrings out depth from his character that is not written down on the page. His sense of torture when forced to shoot an informer from his own ranks is both touching and the touchstone of the film.
The supporting cast of Padraic Delaney, Liam Cunningham and Orla Fitzgerald is also very strong.
The film loses its sense of purpose towards the end when Loach and Laverty examine the division within Irish republicanism that led to brother against brother and family against family.
In one scene, characters reel off dull, political rhetoric. It was intended as a glimpse into the fractious tensions of the time but feels rather more like a party political broadcast.
As one of several films at Cannes which dealt squarely with war - and specifically aimed to make connections with the war in Iraq and its aftermath - The Wind That Shakes The Barley was the most straight-forwardly political.
Loach has lamented that the events of the 1920s in Ireland remain little known outside the country itself.
The Palme d'Or win will ensure the film reaches a wider audience but it is disappointing that his Cannes win comes for one of his weaker films.