"US Isolationism" also did not cause the 1st World War. That had no US role in how it started; before that the US mostly focused on the America's and Asia, to a limited extent, as a young country at the time.
We only got involved because Germany got reckless with their U-boats, we wanted to play dumb about the munitions on the Lusitania, and also Mexico started being stupid because of another revolution/Pancha Villa but was not stupid enough to actually take Germany's offer.
WW2 was caused by Woodrow Wilson being a racist asshole and overall scumbag, Hitler being plain evil and riddled with syphalus, Mussolini being a general fucktard, and Japan letting their imperial aspirations turn their spirit toxic, till we cleansed it with atomic fire.
US 'isolationism' in the interwar years was a return to normal, not a deviation from the status quo.
Only after WW2 did the US military attempt to rewrite human history and historical events to pretend it's absence from the scene caused those wars, in order to help justify things done in the post war years and drive up recruitment numbers by pretending to be more in control of the world and history than they actually are.