Two Thousand Maniacs is a thrilling 1964 horror movie, and you can watch it for free here.
Herschel Gordon Lewis, a pioneer of gore films, directed this classic which stars 1963 Playboy Playmate Connie Mason. The movie is about 6 unlucky Yankees who are lured into a small southern town where the displeased residents kill them one by one, as a form of revenge for the town's ruination during the civil war. I'm normally not one for slasher movies, but the creepiness of Two Thousand Maniacs had me captivated all the way through. I think it's safe to say that Midsommar and even The Wicker Man were heavily influenced by this film.
From Wikipedia:
An all-time great because of all the sadism", enthused Cramps singer and horror aficionado Lux Interior. "The people who act in the movie actually live in the town where it was filmed—they look very inbred. There's a wonderful scene where they take this sexy girl and drop this 2,000lb. rock on her from 20 feet, and the whole town's out there watching. Old ladies all looking, like, 'What are we doing here?'"