Thornton writes, directs and acts in the new film, which takes place in the late 1960s. It looks at how war, life, love and death has affected various generations of one family.
The 58-year-old Thornton gathered an impressive group of his friends to round out the ensemble cast, including Robert Duvall, Kevin Bacon, John Hurt and Robert Patrick.
"All those guys are people I've known over the years," Thornton said. "Once you pick the right people, probably over half your job is done really."
Thornton said he wasn't nervous directing a legend like Duvall.
"You just call 'action' and 'cut.' There's nothing to it," Thornton said.
Thornton will be seen again next month in another ensemble drama. In "Parkland," he plays the head of the Secret Service in Dallas on the day President Kennedy was shot.
The fact that he's drawn to films set in the 1960s is not lost on Thornton.
"Certainly people of my generation revere the '60s and look back on it with fondness, but also, it was a very heavy time," Thornton said. "We look at the '60s as the ultimate for artists."