This Fourth of July, we’ve got a chance to celebrate America’s birth in a very American way — watching internecine warfare, spasms of savage violence and a dark government conspiracy pulling the strings. That’s right, it’s time for a new Purge.

“The First Purge,” the fourth film in the franchise, is an origin story set in modern day New York that allows creator James DeMonaco to do what he does best — mix social satire with doses of heart-pounding horror. It’s a worthy addition to the B-movie “Purge” cannon, even as it’s depressingly prescient.

For those unfamiliar with the “Purge” series, here’s how it works: In a dystopian near-future, the government, led by a nefarious party called the New Founding Fathers of America, allows an annual 12-hour period of lawlessness without recriminations. Over the course of a single night, rape, murder, robbery and everything else is permitted as a way to release anger but also a way to cull an overpopulated nation and lower crime.

Over the past three films, DeMonaco has explored all kinds of different facets to this rich and complex notion, from gun control to the behavior of predatory corporations, to government brutality against people of color and class wars. This time, he goes back to the root of the “societal catharsis” to dive into how murder is incentivized and celebrate the first resistance to the purges.

DeMonaco sets “The First Purge” on Staten Island. He bafflingly attracted Oscar-winner Marisa Tomei to play the behavioral scientist who has designed the purge for the NRA-backed New Founding Fathers of America. She’s not on any side here; she’s just a data-driven gal unwittingly about to unleash hell on an island.

On the ground, we meet our main players: Y’lan Noel, who makes a very charismatic drug kingpin; Lex Scott Davis, as his old girlfriend who has become a community activist; and Joivan Wade as her brother, torn between the lure of quick drug money and his sister’s unwavering morality. Rotimi Paul makes an absolutely frightening psycho.

It is perhaps fitting that director Gerard McMurray, an African-American, directs the story of an inner-city minority community under siege. McMurray has a deft touch juggling action sequences, humor and intimate dialogue.

The first purge actually starts off unevenly, with many Staten Islanders who have stayed choosing to have a block party rather than murder each other. The New Founding Fathers soon decide to goose the violence with a familiar tactic and the film moves into action hero territory, with Noel turning into a hero and our makeshift community banding together to fight an oppressive regime. The blood flows so much that in one sequence it splashes the camera itself.

The “Purge” films have never been very subtle and “The First Purge” is no different. At one point, the ragtag Staten Islanders are being systematically hunted by heavily armed white gunmen wearing KKK hoods or Nazi coats and masks that look like blackface and minstrel shows.

But DeMonaco’s signature hammy scriptwriting also rears its head. The characters are one-dimensional and prone to doing stupid stuff, like wandering out alone during a night of mayhem. Poor Tomei is a wonderful actress marooned. “What have I done?” she intones toward the end, having to use her eyes to convey the turmoil her dialogue cannot.

But there’s no denying DeMonaco’s ability to conceive of a film that seems ripped from the headlines. “The First Purge” is hardly sci-fi in the face of neo-Nazis really marching in U.S. streets, immigration policies that have been denounced as inhumane and a Congress awash in NRA donations.

One thing DeMonaco can’t do is avoid his own timeline. We know that the purges are still raging in 2039, so whatever happens in Staten Island can’t end them. That’s a truly depressing thought on this Independence Day holiday.