I would say American cinema thrived for sure in the 50's and 60's, and forever changed it. Nothing was the same after "Bonnie and Clyde" and "The Wild Bunch", which essentially defined what screen violence would become for the next 30 or so years. Godard was in France changing cinema forever and becoming the most important filmmaker since Griffith. So I'd have to say, in all of world cinema, the 60's changed everything. The 50's may have had the best of what already existed, but didn't redefine nor question cinema aesthetics like the 60's.