Taking Over the Town

A plan for villains who think on a large scale. The bad guys isolate a community from the outside world and then loot it at will.

The typical plan is to cut off communications (e.g., take down phone lines) and then isolate the town (blowing the only bridge in is common). Local law enforcement will be eliminated (often being captured and locked up in their own jail).

Expect at least one hero to stage a Die Hard on an X.

Not to be confused with Take Over the City, which is less about looting and more about control.

Examples of Taking Over the Town include:

Comic Books

In a Golden Age Justice Society of America story, The Injustice Society of the World did this to Washington DC.
Cobra does it to the town of Millville in issue 100 of Marvel Comics' G.I. Joe series.
In an episode of Bruno Brazil, a gang of thieves knocks out the entire population of a town with a large-scale Sonic Stunner.
This was Blacksmith's plan for taking over Central and Keystone Cities in The Flash. She had Murmur and Mirror Master attack radio stations and reprogram their antennas to broadcast a mirror shield around the twin cities to prevent anyone from coming in or getting out.
This is more or less the backstory of Sin City.
Stealth example: In the Batman story arc "No Man's Land", Lex Luthor uses his connections in the US government to shut Gotham City off from outside aid after a cataclysmic earthquake so he can swoop in, buy up most of the real estate, and look like a hero.

Film

Day of the Wolves, a 1971 heist movie that could almost be the Trope Codifier.
In High Plains Drifter, this is what the gang of outlaws wanted to do.
In the Australian film Red Hill the escaped convict destroys the communications tower preventing contact with the outside world, and goes on a killing spree with the town's officers.
30 Days of Night (and the original comic it was based on) featured a clan of vampires that essentially invoked this trope on a town on the arctic circle when the sun would be down for a full month.

Literature

The Gutting of Couffignal by Dashiell Hammett
Goldfinger's plan to loot Fort Knox in the novel Goldfinger has elements of this (the plan in the movie is different).
In the novel Jericho Falls, the government of the United States does this to an American town.
In The Lord of the Rings Saruman, a.k.a. "Sharky," does this to an entire country. When Frodo, Sam and the other hobbits return from their epic quest to destroy the Ring to find the Shire under the control of Saruman's evil Men, they gather the rest of the hobbits and take the place back.

Live Action TV

Krane and his gang do this in the Queen of Swords episode "The Hanged Man".
On Jericho this is what the Ravenwood mercenaries do to a town they invade. They take all the supplies and shoot anyone who opposes them. Since the towns are isolated from the outside world, they do not have to worry about anyone coming to help the townpeople. The people of Jericho try to preempt this by blowing the bridge into town themselves before Ravenwood crosses it.
The Butler gang does this to Hopetoun in the final episode of Wild Boys.

Video Games

This was the set-up for Mad Dog Mc Cree. The stranger (i.e. the player) is told that "Mad Dog McCree and his gang have taken over the town" and that both the mayor and his daughter are imprisoned in the gunfighter's hideout, while the sheriff has been locked up in his own jail by the gang.
The introductory questline for Men and Hobbits in The Lord of the Rings Online involves an effort to protect the village of Archet which is having this done to them by the Blackwolds, a vicious brigand gang that has cut a deal with the evil forces of Angmar. After blockading the gate to Combe, the neighboring town, to prevent the people of Archet from going there for aid, they proceed to launch an assault against the town that is only stopped by the intervention of the village leader's son, his band of hunters, and the player.
Taken to extremes by the Demonlord in Dragon Quest VII. He sealed away nearly every city, country and village in the entire world, subjecting each to a different threat. When the game begins, the only land that hasn't been long consumed by darkness is the Hero's home, and he and his friends must travel through time to Set Right What Once Went Wrong and restore the world, piece by piece.

Western Animation

In the Darkwing Duck episode "Just Us Justice Ducks", Negaduck uses an electronic device to create a force wall cutting St. Canard off from the rest of the world.

Real Life

Townies often assume this is the plan of a bunch of bikers riding into town, whether they actually do it or not.