1939, absolutely.
WWII prematurely ended the Golden Age of Hollywood: Male stars enlisted, and movies became propaganda.
I am not denouncing patriotic, war-time movie making as have my leftist associates of the past (deriding them as jingoistic); I am merely acknowledging that vigorously advancing the artistic state of the still-new art had abruptly ceased to be the focus after 1940.
Some of those movies were still quite good; they just weren’t as consistently or dramatically ground breaking as in 1939 (or, to a lesser extent, 1940).
The 40’-45’ years were propaganda, we made about 80% tinged with propaganda, where as the Germans only did about 20%. There are black and white German films out there that are equal or better than the ones we produced. Their war time propaganda films pretty much mirror our own. (The ones with stories and actors, that have the same themes as ours, including musicals.) One would think here in the USA that we are the only ones in the world that can make great movies. Frankly I’m sick of the crap they produce here. I’d sooner re-watch an old black and while on You Tube. BTW, lately I have been watch the Russian films with WW II themes, they have been pretty good. (With or without sub titles)