Snow White to The Wizard of Oz to Gone with the Wind. The decade Hollywood went from silent to sound and built the studio system that would dominate cinema for thirty years.
The 1930s is the decade that built the studio system. The transition to sound that had begun with The Jazz Singer (1927) was, by the early 1930s, complete; the major studios (MGM, Paramount, Warner Bros., 20th Century Fox, RKO) had consolidated their vertically-integrated production-distribution-exhibition models; the Hays Code was imposed in 1934 and would constrain Hollywood content for the next thirty-four years.
Internationally, the decade is bracketed by the Weimar German cinema of the early 1930s (Fritz Lang's M, 1931; The Blue Angel, 1930) and the displaced refugee directors who fled the Nazi takeover after 1933 to work in Hollywood (Lang himself, Billy Wilder, Robert Siodmak, Fred Zinnemann, Otto Preminger). The European exodus reshaped American cinema profoundly across the following two decades.
Three of the ten films above are from 1939. The year is sometimes called the greatest in Hollywood history. The films released that single year include: Gone with the Wind, The Wizard of Oz, Stagecoach, Mr. Smith Goes to Washington, Wuthering Heights, Ninotchka, Goodbye Mr. Chips, The Rules of the Game (France), Of Mice and Men, Dark Victory, Beau Geste.
The cluster is not entirely an accident. The studio system was at its operational peak; the Code-era constraints had stabilised into a working production environment; the Depression-era audience demand for high-quality entertainment had reached its commercial maximum; the second world war had not yet diverted resources from Hollywood production. The year is, in retrospect, the highest sustained output of the classical studio system before the war reorganised everything.