I'll go ahead and join everyone in linking to this, but when it comes to World War II, there's more than enough terrific stuff to watch, of course. I just watched a bunch of Warner Brothers war cartoons -- they're helpfully collected in the Looney Tunes Golden Collection, Volume 6, Disc 2. Well, that is, most of the cartoons on that disc are WWII-related; I guess they ran out, because there are three postwar Lessons in Capitalism cartoons included at the end of the disc (although then there are three war-related bonus cartoons...I'm not asking for the logic in it). Nor are these the very best WWII Warner Brothers cartoons -- hey, this is Volume 6 we're on, here.
Nevertheless, what these are useful for is getting a feel for what life was like during the war -- what the vocabulary was, what struck them at the time about life at home, what were the stereotypes to play with about being a soldier, and of course the stereotypes of the Germans, the Italians, the Japanese, and their leaders. Well, actually just the Germans and the Japanese; the Italian people really are a no-show, for whatever reason -- which of course, is interesting in itself.
The thing that struck me on watching these was that Hitler is mostly played not so much as an evil madman, but as a bullying buffoon. To me, that's always been the Mussolini role (and when he shows up, he always plays that role). There is a bit of Hitler-as-madman, but relatively little, I thought, either on the examples on V6,d3 or, from what I remember, of the other WWII-era Looney Tunes. He mostly goes into madman mode when he's speaking at rallies, but, for example in "Russian Rhapsody" (1944), in which he falls victim to the same gremlins, now from the Kremlin, who tortured Bugs Bunny in "Falling Hare" the previous year.
The German people are generally both mindless yahoos but also terrorized, clearly afraid to be punished for not Sieg Heiling quickly or enthusiastically enough. They are, of course, easily outwitted by Bugs or Daffy or whoever is playing the Americans; of course, this is the typical Bugs Bunny pose, that Americans are not necessarily stronger but are always craftier than the enemy. About the ugly Japanese stereotypes...well, everyone should be sure to see this stuff once.
By the way, it's not on this disk, but I'm a big fan of watching the Warner Brothers' "Point Rationing of Foods" (1943) a short cartoon made for the government to explain the rationing system. Not only does it help give you a sense of just how thoroughly the war pervaded everyday life, but there's all sorts of stuff that gives you a sense of what food was like in that era, anyway. It's an extra on Volume 3, Disk 3, of the Golden Collection. I'm less of a fan of the "Private Snafu" series of short features about the title character, done for the military. They're neither very funny, in my view, or especially helpful in understanding very much about the war, especially after you've seen any one of them -- although I've only seen, if I recall correctly, about six of the 24 produced, so perhaps others are better. Basically, what I got out of them was that people in the 1940s were amazingly entertained by stuff that seems extremely mildly risque to us, or at least either the Warner Brothers cartoonists or the military or both thought that they would be amazingly entertained by it.
Oh, the other interesting thing about the set of cartoons on Volume 6, Disk 3 is that it includes two anti-war efforts: "Bosko the Doughboy" (1931), and "The Fighting 69 1/2th" (1941). The first is a fairly standard interwar anti-war effort. The latter is mainly interesting because of its late date. It features two ant armies pointlessly fighting over a picnic, complete with WWI-type trench warfare, and no good guys to root for; this is a world where war is all pointless squabbles between people who should just grow up and learn to share, a lesson that was very much Off Message soon after -- in fact, I'm surprised that FDR-supporting Warner Brothers would have released this as late as 1941.
In case you're wondering, all Warner Brothers cartoons get my highest recommendation. Well, OK, I mostly could do without Bosko and the other early ones, but even those have their charms.