Quite simple really - The Wall Street Crash of October 1929 never happens.
I'm no expert on economics, so I'm not sure what could have prevented it, but I'm more interested in the political and social results, so let's just say that for some unknown reason, the crash never happens. Maybe the world economy experiences recessions over the next few years, but nothing like on the scale in OTL.
What effects would this have? Would Hitler and other dictatorial regimes have risen to power? Would Woodie Guthrie have had a career? What other things might have worked out differently?