To commemorate the two-hundredth anniversary of the Peterloo Massacre—the violent disruption of a peaceful demonstration for political and economic reform that occurred in Manchester, England in 1819—Mike Leigh has made what amounts to his first epic. And despite the fact that “Peterloo” is unwieldy and long-winded, it’s also quite stirring and memorable.

First, the history lesson that most American viewers will require—and probably a lot of British ones as well. After the defeat of Napoleon at Waterloo in 1815, more than 300,000 soldiers and sailors returned to civilian life in England. The situation was especially acute in the country’s northwest—the industrializing region of Lancashire surrounding Manchester, the center of textile manufacture. It depressed factory workers’ wages and contributed to high levels of unemployment there. Meanwhile the so-called Corn Laws, designed to help landowners by keeping a floor under grain prices, were strengthened, prohibiting the import of foreign grain if domestic prices fell below a certain level. This policy, of course, created a strain on workers’ household budgets.

The economic situation was exacerbated by the fact that, as a result of electoral practices that dated back to the fifteenth century, industrial centers like Manchester enjoyed no parliamentary representation. The right to vote even in rural areas was, moreover, extremely limited, and so-called rotten boroughs—virtual ghost towns whose MPs were effectively appointed by the local bigwigs—proliferated.

In the post-1815 era, the Tory administration of Lord Liverpool, in concert with the notoriously profligate Prince of Wales, who was then regent for his mentally unstable father King George III, were determined to maintain this status quo, which essentially meant continued rule by the landed aristocracy over the expanding industrial regions. It was against such a backdrop that agitators in Manchester and throughout the country demanded reform, particularly in suffrage and parliamentary representation, which if effected could also bring legislative change. Thus the mass demonstration at St. Peter’s Field in Manchester was mounted, bringing tens of thousands together to voice their anger over the situation. Invited by the locals to speak to the crowd was a famed radical orator of the day, Henry Hunt.

The local magistrates, the justices of the peace, literally read the Riot Act of 1714 to the crowd, commanding them to disperse, and then ordered in the military—first the local yeomanry, an undisciplined militia of armed volunteers on horseback, and then regulars from the forces of the Northern District. In the resultant melee up to fifteen people were killed and hundreds injured.

In recounting this story Leigh refuses to mold the narrative in a conventional fashion, focusing on a few characters (like, for example, “Spartacus,” another tale of reaction to oppression), preferring instead to introduce figures, some real and others fictional, and then bounce around from one to the other. A few become fairly prominent, but even they cannot be called the major characters, remaining instead parts of the large, fluctuating ensemble.

Thus the film is bookended by sequences featuring Joseph (David Moorst), who is first shown staggering about on the field of Waterloo and tramping back to his father, mill-worker Joshua (Pearce Quigley) and cynical mother Nellie (Maxine Peake), and futilely searching for work in Manchester. He’s clearly suffering from what today would be diagnosed as PTSD, and even when he attends radical meetings with his father, he seems bewildered. Joseph will be one of those killed at Peterloo, apparently modeled after John Lee, a Waterloo veteran actually killed there. But though he clearly represents the lower classes that are used by the powerful and then treated shabbily, he’s hardly the film’s protagonist, disappearing for long stretches, though his continued wearing of his military red coat sets him apart visually, rather like the girl Spielberg employed in “Schindler’s List.”.

Nor is Samuel Bamford (Neil Bell), the local agitator who, along with his friend Joseph Healey (Ian Mercer, whose boozy face Leigh loves to train the camera on), persuades Hunt (Rory Kinnear) to come to Manchester. A good deal of the film is devoted to antagonism that develops between Bamford and Hunt, who’s portrayed as an arrogant, well-to-do champion of the downtrodden, over tactical preparations for the rally—especially whether defensive weapons should be present (Bamford for, Hunt against) while the orator is housed with nervous Joseph Johnson (Tom Gill) and his wife (Lizzie Frain) and tries to get some peace and quiet to write his address.

What’s abundantly clear is that for Leigh, these people, and the many others who cluster around them, are, whatever their individual flaws, the heroes of the piece, standing up for the rights of the low-born against a repressive and capricious regime. The characters on that other side are depicted in broadly satirical strokes as brutal villains. At the top of the list are the decadent Prince Regent (Tim McInnerny) and his political allies, the unctuous Liverpool (Robert Wilfort) and venomous Home Secretary Lord Sidmouth (Karl Johnson), who are anxious to bestow a huge bounty on the Duke of Wellington while leaving the poor to starve. Little better is John Byng (Alastair Mackenzie), military commander of the Northern District, who passes the responsibility of keeping order at St. Peter’s Field to his lieutenant so he can attend a horse race.

As awful as these men are, in Leigh’s portrayal, even worse are local magistrates Fletcher (Philip Whitchurch), Hay (Jeff Rawle), Norris (Martin Savage), Ethelston (Vincent Franklin) and others of their ilk, who conspire with vicious Constable Nadin (Victor McGuire) to spy on radicals and summarily imprison some of the ringleaders. (It’s characteristic of Leigh’s approach that he doesn’t disclose the prisoners’ fate, simply leaving their story hanging.)

In jumping from character to character and plotline to plotline, “Peterloo” often feels rather meandering and shapeless but, while hardly impeccably structured, it builds up a considerable head of steam by the final stages. Still, the narrative raggedness can be irritating, and some viewers will undoubtedly find much of the dialogue too politically heavy-handed. It leaves absolutely no doubt where Leigh’s views lie (not only about the circumstances of 1819 but about those in contemporary Britain), and as the film proceeds you may come to feel that in his screenplay it’s not only Hunt who shows a penchant for thudding rhetorical overstatement.

That undermines some of the performances, though generally the actors fulfill Leigh’s requirements, whether it means going a full-bore satirical route for the villains or striving after a homely directness among the mistreated working class; it’sd their joint effort, rather than their individual contributions, that matter. Though epic in scope, the picture eschews the lushness typical of the work of a David Lean; Leigh’s style is rougher and grungier, deliberately sidestepping any hint of slickness—an approach that editor Jon Gregory easily falls in with, as also do production designer Suzie Davies and costumer Jacqueline Durran. Cinematographer Dick Pope may not achieve quite the same painterly effect he did working with Leigh on their masterful period biography “Mr. Turner,” but he gives the Manchester sequences a gritty, Dickensian feel that contrasts well with the more opulent look of the royal palaces and parliamentary chambers back in London (as well as the Ascot appearance of Byng’s horse race).

For some “Peterloo” will come across as more of a harangue than a drama, but even so it carries an undeniable punch–an impassioned film with a clear, unambiguous point of view, which it presents strongly and without apology.