I think the big war movies from the 60s represent the peak of ensemble casts. Even the Dirty Dozen had Lee Marvin, Bronson, Telly, Sutherland, George Kennedy. Ernest Borgnine and Jim Brown.
Orlando Bloom and Tom Hardy before anyone knew who they were. Tom Sizemore, Eric Bana, Ewan McGregor, Sam Shepard, Josh Hartnett, Jeremy Piven, Ron Elard and quite a few “that guy” actors.
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More recently this one stands out:
https://www.imdb.com/title/tt0057115/
and maybe the Magnificent Seven
Jiminy Christmas