Reassuringly, the two golden ages of American film each arrived in the wake of utter chaos. The roughly simultaneous advent of talking pictures and the Great Depression ushered in the glories of the 1930s; decades later, the collapse of both the Hollywood studio system and American optimism in Vietnam helped soften the ground for such 1970s classics as “Chinatown,” “The Godfather Part II” and “The Conversation.” And those particular gems weren’t just great movies from the ’70s. They were,...