To me it seems that the culture of the 1930s flowed seamlessly into that of the early 1950s. There's that oft-quoted thing about people thinking The Wizard of Oz is a Fifties film (actually it was made in 1939). The style of filmography, the sounds of popular music, and so forth, show far more similarities between the 1930s and early 1950s than between the 1920s and 1930s, or certainly between the early 1950s and the mid-1960s. Presumably this stasis can be attributed to the traumatic effects of the Second World War: a lot of the male population suddenly being jerked out of its usual position (and the women, for that matter, in different ways) has got to both slow down the usual cultural progression and furthermore to instil values of conservatism and nostalgia for the pre-war world that discourages change.
So let's say there's a 1940s without the Second World War. The Great Depression still happens (otherwise the Thirties would be nigh unrecognisable) but for whatever reason, German revanchism and Japanese and Soviet expansionism only account for a few minor conflicts rather than a world war.
With that in mind, how do you think the culture of the 1940s and 1950s would have looked?