Hitler invaded Czechoslovakia and the international community did essentially nothing about it. It both emboldened him for further invasions, and provided him a huge manufacturing power to pump out tanks and armaments. If the international community said "Hell no, we're defending Czechoslovakia on principle because that invasion is BS", they would have fought a much weaker Germany and very likely prevented WWII (or at least one nearly as bad). Frankly I don't see how you can argue that's not an extremely apt comparison.