Why would that lead to the allies losing if the US enters WWI on the side of Britain and France early? I don't understand how that would be possible. Now US siding with Germany would certainly but I'm not sure how early US involvement in WWI on the side of Britain and France hurts them.
Because: politics. Basically, the US enters the war less prepared than in OTL due to the Preparedness programs not being implemented yet. It takes a while for the US to mobilize but the Allies are begging for American troops. And so a first wave comes over prior to the main brunt of American soldiers.
These Americans are intagrated into the already established British and French forces instead of being seperate under their own command (something both the French and British wanted in OTL but didn't get). Unfortunately, the American soldiers are used - in the eyes of the American media and public at least - as cannon fodder. Jokes abound about how "The King has vowed to fight to the last American!"
By the time the main American forces arrive, they've learned their lesson, and American troops are serving under American generals. Unfortunately, there is now a desire to show what American troops can really do if given a shot, and this leads to some ill-conceived battles where the Americans get throughlly bloodied.
By this point the US public has grown sick of the conflict and a Republican peace candidate becomes elected President in 1916. He negotiates a separate peace with the Germans which gives the US enough face saving clauses that they can turn around and say that American honor was upheld.
Of course, suddenly having the Americans leaving, throws the Allies lines into chaos and convinces some fence sitters such as Italy that the Allied cause in doomed, so they throw their hat in with the Central Powers.
It ends up just being a mess, and probably leads to years of acrimony between the United States and it's one-time allies, as well as a German victory.
There's more too it and, as I said, I'd need to do a LOT more research to make it work. But that's the outline at least. Pretty much it started out as an idea to counteract all of the "America Gets Involved Early and Save the Day" timelines that I've seen over the years.
