The anti-German sentiment during WWI may stem from a larger ammount of sabotage which occurred on American soil caused by German agents. For instance the explosion of the Black Tom munitions factory.
Were they? German immigration peaked 35 years before the U.S. entered World War I. In the 19th century, German immigrants were elected the governors of New York, Pennsylvania, Illinois, and Wisconsin.
After WWI the AEF just came home. After WWII the USA stayed in Germany as an occupation force for several years until the West German government got on its feet.
This gave people a chance to get better acquainted with individual Germans and discover that most of them were pretty much ordinary people.
The disturbing thing is that ordinary people could support a regime like the Nazis, although subsequent research has demonstrated that all of us are pretty much like that under the wrong circumstances.
I do think the close association with Germans by US army troops was a big factor. I don’t believe there were many post WWI German war brides, if any.
As I said, there were some (in raw numbers, quite a few) German immigrants earlier than the peak years. Hell, there were Germans here before the Revolution. Some were certainly assimilated, and the more recent immigrants provided an important voting bloc in some states.
But it is flat out wrong to say, as someone did here, that they had ''largely arrived by the mid-19th century" As my graph shows, the massive waves of immigration were post-civil war, and peaked later. Relatively little immigration took place before 1860.
In 1914, most people of German descent in the US would have been first or second generation. As others have said, at that time, German enclaves spoke German, published German newpapers, belonged to German organizations, and drank beer. They had identifiable ties to the Old Country. All of this was outside the mainstream, and easy to demonize. It is no coincidence that these massive numbers of immigrants coincided with increasing political movements to impose prohibition.
By 1939, much more assimilation had taken place. Ironically, part of the reason for this was the anti-German feeling we are discussing. Germans changed their names, stopped speaking German, and their organizations (as a rule) adopted a lower profile. They were much less scary and new in 1939.
I think David’s got it. 
Add to that the fact of the Russians were oppressing East Germany big time while we were busy rebuilding West Germany. It turned our hatrid away from the Germans and toward the new bad guy.
The post-World War I spillover might more accurately be described as anti-radical and anti-immigrant, rather than anti-German. Demonization of Germans faded quickly after the armistice, because reds and radicals represented a more immediate threat.
Radicals really were a threat in war-ravaged Europe; Communists took over Russia and for a time in 1919 appeared poised to win Hungary and Germany as well. In the US they were paper tigers, but a few over-hyped bomb scares and a lot of labor unrest (caused by postwar inflation and unemployment) fueled the 1919-20 “Red Scare”, in which thousands of mostly eastern European aliens were arrested without trial and deported.
Anti-immigrant sentiment continued into the 1920’s, which saw the revival of the Klan, the repeal of voting rights for non-citizens, and the drastic reduction in immigration via the Johnson-Reed Act of 1924.
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Nineteen Eighty-Four. It’s been a while since I read Brave New World, but I don’t remember any war going on there; whereas in the other, Eurasia was permanently going at it with either Eastasia or Oceania, but never both.
We’re not an occupying force anymore, but fifty-one years later there is still a major presence in both Germany (75,000 troops) and Japan (45,000). We still have roughly 40,000 in South Korea.
Random writes:
> But it is flat out wrong to say, as someone did here, that they had ''largely
> arrived by the mid-19th century" As my graph shows, the massive waves of
> immigration were post-civil war, and peaked later. Relatively little immigration
> took place before 1860.
Now you’re the one who’s exaggerating. There were two peaks, one in 1854 (221,253) and one in 1882 (250,630). It’s certainly not true that “relatively little” immigration took place before 1860." There’s no way to tell from the few statistics given so far whether the total number of immigrants before 1860 was more or less than the total number of immigrants from 1860 to 1917. Germans began to migrate to the U.S. in significant numbers in 1709. The fact that one year in the period 1860 to 1917 was somewhat more than the highest year in the period 1709 to 1860 doesn’t prove that the total number from 1860 to 1917 was higher than the total number from 1709 to 1860. Does anyone have the complete set of numbers of German immigrants from 1709 to 1917.
Frylock writes:
> Was there a cynical and mean sounding realpolitik-al reason for him to want to
> do this, or was he just being cool?
What point are you trying to make here? Do you think that Roosevelt gave press conferences while wearing a beret and sunglasses, sporting a soul patch, while jazz played in the background, where he announced that he had appointed some German-Americans to be generals because he thought they were really cool? I suppose that realpolitik might be an accurate description of his reasons. Roosevelt was a compromiser and not an ideologue. He tried to keep as many people sufficiently happy with his policies while he got as much of his agenda passed as was possible.
The town where my parents live, Long Valley NJ, used to be called German Valley. Until WWI.
When WWII happened, the town was already called Long Valley, so there wasn’t much else to do. 
I started off kidding, but the more I think about it the more I think I might be on to something here. After the previous German backlash during/after WWI, what more could be done about Germans in general during/after WWII?
Plus, beating the snot out of somebody sort of takes the fun out of hating them. The Allies eventually drove zee Germans back to Berlin. We don’t hate the Japanese any more (do we? auto makers aside). If we had taken out Osama bin Laden a month after 9/11 along w/the rest of the Taliban, would there be as much anti-Muslim sentiment as there is today?
We need a “Thinker” smiley.