France loses badly in WW1. The ensuing revolution mutates from leftist socialism into fascism. The new regime brutally consolidates power and builds up industry and the armed forces. The Great Depression happens roughly the same time as OTL. The US, in economic disaster, is unable to respond to French attacks in Central and South America (The French also attack Siam). Seeing it's southern "backyard" fall to revived French imperialism, the US declares war anyway. By the mid 30s, the US economy has somewhat recovered due to the growth of the military industry, but it is too little too late and the stalemates at sea and in the jungles result in the 1934 Treaty of Dublin which recognizes massively increased French dominance in Central and South America, the Caribbean, and the Philippines and the Pacific (as well as Siam and southern China). The US does however gain Saint Pierre and Miquelon. The British remained neutral throughout the conflict in fears of a revolt in Quebec and also to focus on rebuilding its struggling economy. Italy, Spain, Greece, Poland, Austria, and even Portugal eventually enter into a Fascist alliance lead by France following its stunning victory. By the end of the 30s, this ATL Axis is aligned against Britain and Germany. Austria dreams of reclaiming Yugoslavia, Hungary, and Czechoslovakia (and maybe Bavaria one day too?). Italy conquers Albania and Ethiopia. France wants to split Belgium with the Netherlands (not to mention taking over the Congo). The French also transfer some of their new conquests in the Americas to Spain and Portugal to ensure their continued support. The USSR serves as a boogeyman in the East. Bulgaria, Romania, and the Scandinavian countries remain aloof. Iran and Afghanistan become interested in aligning with the French to counter the enormous British and Soviet presences on their borders. Turkey hates the British, the Soviets, AND the French. Japan begins hoping the europeans in south east asia will slaughter eachother so that the Rising Sun can swoop in and liberate Asia in the ensuing chaos. America is shocked and demoralized by its loss of the southern Western Hamisphere to French fascist imperialism.
Hack away at this. I'm sure its full of errors somehow.

Would make for an interesting 1930s French Fascist wank though...
wait, wait, wait... shit. i forgot the whole Germany wins WW1 part... so belgium is dominated by Germany and the congo is probably in German hands. A handful of French colonies have also probably been handed to Germany. In this ATL i suppose Germany is somehwere halfway between the Imperial Germany of WW1 and the Weimar Republic of OTL. It needed to introduce a bunch of reforms in order to survivie the Great Depression.
anyway it's all just a bunch of food for thought for the OP. goodluck making a TL