But, as for the stupidest war in American history, I'll take it ahead of even Vietnam. And you should too, if you know the big picture. That includes knowing that the U.S. had even less national interest, in Realpolitik terms, in World War I than any other imperialist or non-imperialist war in history.
In case you're wondering, beyond the Luisitania or "unrestricted submarine warfare," what the final tipping point was, especially away from the British-tilting East Coast and especially in the Southwest, read this piece.
Related? The Lusitania was "technically" a passenger ship. It was also carrying small arms, ammunition and other munitions and that was known to people in a position to know in the U.S., British, and German governments. It was also armed with guns big enough to sink a submarine that tried to follow the letter of international law and surface and halt it.
Second, and speaking of? The British "blockade by extension," blockading the Netherlands, Denmark, etc., to keep them from importing goods above peacetime levels and reselling them into Germany, was as illegal under international law as was Germany's declaration of submarine warfare and sink-on-sight submarine blockade zones. In fact, matters similar to this are why we had gone to war with Britain 100 years earlier. But for Wilson, freedom of the seas was selectively enforced.
Here's how it worked, in the rough, from this Aug. 4, 2014 blog post of mine. If Denmark imported, say, a total of 100,000 pounds of wheat a year, on average, from, say 1900-1913, then in 1915, that's all Britain allowed. It couldn't import an additional 500,000 pounds, with the presumable intent of then exporting the surplus to Germany.
Third, there was no "bad guy" like Hitler in World War II. (That said, we had a "bad guy" on our side in Stalin then!) The most repressive governments? As in WWII, one was on each side — Tsarist Russia before the March Revolution, for the Allies, and the Ottoman Empire for the Central Powers. Pre-war, Hohenzollern Kaiser Wilhelm II was moderately authoritarian, but no more than moderately, and certainly not totalitarian.
Now, the Germans did burn the library at Louvain, Belgium. They did shoot franc-tireurs. Both illegal under international law. Bayoneting babies? Allied-American propaganda. They did also, tis true, shoot Edith Cavell. And? She had been duly convicted of being a spy. And she WAS a spy. Bad PR for the Germans? Of course. Unlawful? Not at all.
As for the "German war guilt" the Allies pinned on it afterward? Bullshit. Basically, Austria-Hungary and Serbia roughly tie for first on causing the war, with Germany running a somewhat distant third on what was a highly overdetermined conflict, as I note at the bottom of a roundup of some of the best — and some of the worst — books about World War I.
National interests? We had none. Germany never could have gained the type of mastery that Hitler aspired to, or that Napoleon briefly had. And, realistically, they weren't aiming at that level of control. Sure, they had greedy eyes that got bigger as the war lasted longer, especially in the East. But, already going back to Venezuela in the 1890s, Wilhelm had basically tried not to tangle too much with the Americans. And, without tanks, with artillery all still horse-drawn, they couldn't have done a Blitzkrieg to get to that point of domination.
Yes, it's true that Germany had various agents in Mexico during that country's revolution, per the story at the top link. But, until the time approaching the Zimmerman Telegram, they weren't planning to foment an invasion of the U.S.
Finally, this was the first, but far from the last, fateful plunge into "entangling alliances" that George Washington had warned about in his Farewell Address.
Related to that is some Realpolitik. We had one vital national interest in World War I. And that was letting the Entente and the Central Powers beat each other fucking senseless as long as they were determined to so do.
What would have happened had we stayed out — specifically, if Wilson (or a better President; he ranks below average in my book for many reasons, and Scott Berg's bio of him is atrocious) had warned Britain early on to stay away from the blockade by extension?
Probably, Britain would have gone ahead, gambling it could starve out Germany before Germany could do the same to it.
A truly neutral president would have then forbade American-flagged vessels from traveling into any war zone, and let the Allies and Central Powers beat each other senseless.
Assuming the Germans still smuggle Lenin into Russia, on a sensical view, the British double down on the blockade in 1918 while sending out peace feelers at the same time. France gets dropped a British hint and reluctantly falls in line. Germany decides to play defense rather than fight the Kaiserschlacht that Ludendorff and Hindenburg call up in 1918, with no Americans to face. That, then means more German farm horses still in place, and the British blockade doesn't bite as much. But Austria, war-weary, pushes it, and Germany sees Lenin trying to export the revolution, as he actually did. Italy and the Turks are both exhausted.
With luck, everybody heads to the table, and on the western and southern fronts, accepts a treaty like the Treaty of Hubertusburg that ended the Seven Years War. In the southeast, they agree to toss the Karađorđević dynasty in Serbia for the old, pre-1903, Austria-friendly Obrenović house.
Option two is much more pessimistic. Nobody lays down their arms. Lenin uses diplomatic immunity — or other means — to start the revolution in France and Britain, just like in Germany and Austria-Hungary.
Still, that revolution, even if successful all across Europe (doubtful) wouldn't have toppled the American government.
In either scenario, the U.S. isn't further glorifying citizen war in general and World War I participation in particular with Armistice Day, later Veterans Day. Americans wouldn't have absorbed the British romanticizing of the not-so-Great War, either. That romanticizing tends to overlook things like shell-shock, PTSD of a century ago before we knew what PTSD was.
That said, per all the above, World War I is fertile ground for alternative history buffs. Here's a sample of mine related to the Caribbean. Here's a much longer one, related to Sarajevo and Gavrilo Princip.
At the same time, per the old song, "How ya gonna keep em down on the farm after they've seen Paree?" it was indeed true.
See how military service transformed veterans from a small county in north Texas.