Deviation Actions
One scenario for a massive Second American Civil War in the Great Depression era: America did not join WWI, and it ended in a peace of mutual exhaustion by 1919. With all European powers utterly wrecked economically from five years of total war (and resenting the US for their isolation in the Entente case or for selling weapons and financing the Entente in the Central Powers' case), America would not receive the needed investments from the European powers which was critical to their post-war economic boom in the 'Roaring Twenties'. That could had led to an even worse Great Depression for America if/when it hits, in turn leading to greater political radicalization and social instability. Add to the lack of an FDR presidency (Say he got assassinated or succumbed to illness earlier), and you may get conditions ripe for civil war.
Worsening things would be if as a result of 'allohistorical butterflies' the Palmer Raids never occurred (and thus the IWW and other Socialist organizations and parties are never crippled beyond repair as political forces), and D. C. Stephenson's crimes were never discovered leading to his conviction (and thus the KKK and other ultranationalist groups are never affected by scandals and remain legitimate and acceptable in the eyes of the public). That would lead to much stronger far-left and far-right in the US, which could come out of the woodwork and becoming factions in a potential civil war if it erupts.
I think 1929 is a bit too early for things to have spiralled out of control to the point of civil war and then worsening to quite literally 'Warlords America', but that's just my view, and I don't have enough context for your scenario (beyond an even worse 'Black Friday') to say whether a rapid collapse into a disastrous multi-sided civil war is impossible. You may be interested in the alternate history timeline "The Falcon Cannot Hear" which depicts a multi-sided US civil war in the late 1930s to early/mid-1940s similar to your scenario.