Here's a rough outline of a scenario that might do it:
Firstly have the First World War drag on for several more years, with the US becoming more heavily involved militarily. A US intervention in Mexico in 1918 results in several Latin American countries coming to Mexico's defence and joining the Central Powers, opening up an American theatre and resulting in the US occupying Mexico.
In the 1920 US Elections, where Wilson attempts to run for a third term, the Democrats are defeated in a massive landslide by the Republicans who campaign on a pro-peace platform, resulting in the US pulling out of the war, with the US establishing a puppet government in Mexico. With the US out of the war the Central Powers win the Great War. In the aftermath of the War Britain and France both experience radical socialist revolutions similar to Kaiserreich, and as a result Canada falls into the US's orbit and later becomes integrated into it, whilst France and Britain's Caribbean possession become territories and protectorates of the US.
Over the course of the 20s things go pretty much like they do in Ruins of an American Party System, with the Democrats steadily collapsing and the Republicans becoming dominant, whilst the country goes to hell in a handbasket, only this time there are a bunch of demobilised soldiers running around adding considerable fuel to the fire.
When the depression hits the Republicans prove incapable of adapting to the situation and mishandle spectacularly. As a result the military steps in and declares a state of emergency in a coup. Whilst many support the move in the name of bringing stability and the belief that desperate times call for desperate measures, there are also plenty of pro-democracy/anti-coup factions, and sooner or later the US is bogged down in a Civil War. In order to bolster their support the military government forms an alliance with the various right-wing militias in the country. The military government eventually wins, and with the various progressive and democratic factions in the country purged, and the far-right in ascendency, the government develops a para-fascist ideology to shore up its legitimacy, blending elements of fascism, American exceptionalism, manifest destiny, anti-socialism, populism, and technocracy.
The military government responds to the problem of the Depression and post-civil war reconstruction through mass militarisation and rearmament, similar to OTL Nazi Germany. National Service is introduced and the unemployed are mobilised for public works projects, industries owned by anti-coup businesspeople are siezed by the government or given to coup supporting businesses, anti-coup trade unions are shut down and independent labour organisations are turned into institutions for disciplining workers that combine the scientific management principles of Taylorism and Fordism with military discipline, and the armed forces are greatly expanded.
In terms of foreign policy the USA's short-term goals involve establishing total dominance over the Caribbean, Central America, and Northern South America (basically the proposed American Technate), for the purposes of establishing total autarky and self-sufficiency as well as ensuring total domination in the Atlantic and Pacific, whilst their long-term goals include countering the rising power of Japan, destroying European socialism, and securing America's rightful place as the dominant world power.