So, one of the features of studying things like biological species or languages, is that they're not really things. Or rather, they are things, but in a fuzzy, not-very-thingy kind of way.
What I mean is that it is often difficult to define the exact boundaries of a species or language. Fundamentally, this is a consequence of the fact that we are trying to apply discrete labels (such as "English" or "Moloch horridus") to populations of things (speakers or individuals) that exhibit a degree of variation (e.g., dialects or subspecies), and that change over time.
For example, I can easily read a newspaper article written in the 1950s. I can read something from the 1700s and understand it, but it might sound weird. I can read Shakespeare and understand it, but I probably make use of a lot of the footnotes. By the time I'm reading Chaucer, some things might look familiar, but I probably require help to correctly understand most of the words. So, while those texts are all, in a sense, English, the gradual process of change means that the English of 800 or 1000 years ago is as foreign to me as contemporary French or German.
The same is true of biological species. In that context, people sometimes refer to "diachronic species," which is a way of breaking up a single, continuous biological lineage into subsections that can be given different labels. Given enough knowledge of the biology, one could use not-completely-arbitrary criteria to decide whether two individuals in the same lineage (say, where one was a distant ancestor of the other) should be classified as members of the same species. However, defining break points along the lineage to define species is an inherently arbitrary exercise.
This change process is also true of other (non-linguistic) aspects of culture. There is clearly a continuum of American culture stretching back from the present into the past. And each additional year that we move back, the more the culture seems foreign to me. But how far back is far enough to where you would actually call it a different culture? Again, there is an inherent arbitrariness here that means there is no real answer to the question. I suspect that if you were to take a survey, people's answers would depend a lot on how old they are.
However, I want to make a pitch for World War II being the natural break point in American culture, if for no other reason than that it would provide a psychological distance that would assuage my discomfort with this video from 1942.
Now, I don't know what came up for you, but at the time of posting, the related videos that pop up at the end include classics such as "Nazi Duck" and "Bugs Bunny Nips the Nips."
Also, what's up with the 1942-era shape of Elmer Fudd's head?