1920s USA without joining World War 1

You have to look at at a few things after the war to decide how the US looks and what it is doing.

1. What is going on in the Pacific. Maybe in the peace that is done the Germans does not want to give up all of its islands in the Pacific and ends up selling some of them to the US to get some cash after the end of the war. Remember one thing and that is that the Japanese did not have the casualties like the Entente did, and as a consequence of this they decide that they do not deserve the gains they got at the end of war. They are still not the Western European white folks like everyone else.

2. What kind of peace is in Europe at this time. If both sides are exhausted and there economies are in shambles, the US would be the top economy in the world and if the Entente or Central Powers were smart they would invite American businesses in as partners with there own to help their economies. Oil companies would be an example, they would work with the Central powers to build up their supplies and infrastructure.

3. The 500 pound Bear in the room. What is going on in Russia? Does the US send in an intervention like they did IOTL, or do they just ignore it? Think of the possibilities with Wilson in charge. He could decide that he is helping the local non bolshie factions to self determination. If the Soviets do take over like IOTL I can still see the red scare and such happening because of what is happening in the world.

4. Mexico, do we have a serious problem down there or is it just like it is in our history? If it is worse then the Army will be involved and I can see Militia units being called up depending on how bad it is down there, and serving as long as they did in WWI. You would not have the experience like they got in WWI but more like the Marines had in the Banana wars and in Asia like in the 20's and 30's. Maybe a earlier counter insurgency doctrine that is well developed.
 
in general, you'd think that America would stay rather isolationist, parochial,

Possiblly, tho the isolationist thing applied far less in the Pacifc/Asian region. US Naval and Army units were sent on various interventions. The dispatch of a US fleet, Marine brigade, and Army regiment to Shanghai in 1927029 is one example. The long running permanent stationing of gun boats, Marines, and the Army 15th Infantry Regiment in China had little effective political opposition in the US

and the military would fall further and further behind the rest of the west...

The army ground forces would. I expect the airforces would develop as in OTL, and the USN was on a development trajectory long before WWI that was to take it to the top five in world naval powers. WWI had little long term influence there.
 
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