United States vs. Entente and CP - who would win?

Okay, before some of you guys start yelling "ASB!!!", I'd like to note that this is supposed to be a hypothetical/theoritical scenario, not a realistic one.

In 1914, when various world's great powers start declaring war on each other, the United States decides to completely stay out of the war. But nonetheless, it also starts mobilizing and drafting, just in case. The United States keeps refusing to accept either the Entente's or CP's invitation to enter the war on their behalf. Meanwhile, this WWI proceeds pretty much in the similar way as OTL: Japan and Italy are on Entente's side; the Western and Eastern fronts are pretty much stalemate, while the CP was pushed back on the Pacific, African, and Middle Eastern fronts.

Now, what if, after years of mobilizations and observing the Entente and CP bled each other, the United States decides that they have been weakened enough, and declare war on both?
(by "both", I mean all of them: Britain, France, Russia, Germany, Austria-Hungary, Ottoman Empire, Japan, and Italy)

Let's say this is happening in 1919 or 1920, when either Entente and CP have been repeatedly failed to make a major breakthrough, and facing economic and societal collapse back home, as well as military mutinies everywhere, agree to declare a ceasefire.

Will the United States win?
 
There isn't the slightest chance of the US declaring war on the participants of both sides so the outcome isn't one to worry about...it required years and the final provocation of the Zimmerman Telegram to convince Woodrow Wilson, let alone Congress, to declare war on Germany.
 
There isn't the slightest chance of the US declaring war on the participants of both sides so the outcome isn't one to worry about...it required years and the final provocation of the Zimmerman Telegram to convince Woodrow Wilson, let alone Congress, to declare war on Germany.

Well, yeah, that's obvious (and I think everyone here has already known about that). But, like I said, this is meant to be a theoritical exercise, not a realistic alternate timeline.
 
The U.S declaring war on all sides is effectively the same as the U.S fighting on the C.P side. It does not have the ability to invade mainland Europe, and therefore does not have the ability to damage anything the central powers care about. Instead, it is going to go after Canada and various colonies, fighting mainly against Britain and Japan. Given how war-weary everyone is, you'll probably see colonies offered as concessions fairly quickly to end the war, though the U.S will incur great hatred as aggressors and opportunists.
 
Without US loans and supplies, Entente warfighting capacity is reduced. Under these circumstances I can't see the war dragging on past 1917. Also, you can't hide mobilisation, the British would be very, very wary. Maybe the US can occupy parts of Canada, but it won't be a cakewalk. Europe is quite safe, the USN would get slaughtered if they try an invasion. In the Pacific, the Japanese are not war weary, their Fleet is far more experienced, and US army docrine has not evolved further than the Japanese one.
It will be a very ugly war. Such a naked war of agression on that scale wouldn't be that easy to sell, and will probably lead to collapse and revolution.
 
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