The inaction of the Western democracies during Spain’s communist uprising mirrored their inaction ten years earlier when Germany and Italy underwent the same strife.
The non-aggression pact between Stalin and Hitler floored the West; that wasn’t part of their plan...
You give them way too much credit, I don't think they had a plan, they were floundering from one crisis to the next, with the only clear idea that they wanted to avoid another war at all costs.
Sort of like our previous president in that regard.
They also hoped the League of Nations might be more effective than it proved.
On the Hitler-Stalin non-aggression pact, you might remember that leading up to it Stalin held, in effect, a bid-off with Britain & France bidding against Hitler, and Hitler made him the better offer.
But it's hard to say what the Brits might have done differently, historians say Brits were too arrogant and condescending with Stalin, but I suspect they just didn't have anything of major value to offer him, compared to the risks.
And there's no telling if anyone foresaw in the summer of 1939 what Hitler might do just two summers later.