Easy for you to say - in 1938 most of Euroland was still licking their wounds from WWI, were still broke or owed $$$ to USA, and they couldn't fathom more bloodshed. So the idea of actually attacking Germany in '38 or '39 was just not supported by the populace.
The Poles tried intervening but they were busy getting shellacked.
Sorry I dont know the html for hot linking.
The point was, what are the lessons of history that apply to containing aggressor nations like Iran, NK, or even China, today?
We can wait until we have a full on war that directly or indirectly hurts us as a nation, or we can use whatever means short of war (economic, political, military force) to deter or stop those bad actors from doing worse harm if left unchecked.
Dealing with evil will always have a price. Pay me now or pay me later.