When Hitler started openly violating the Treaty of Versailles and rearming Germany, it was during the nadir of the Great Depression. Britain had suffered a lengthy period deflation and unemployment even before the Great Depression hit -- they never really recovered from World War I. France wasn't worried because they were so much stronger, which, they were. The French loss was a combination of inferior tactics and lack of will.
France and Great Britain knew what was going on with rearmament, which actually began secretly even before Hitler took power, but liked having a re-armed Germany as a buffer against Soviet expansion.
Plus, Hitler's rhetoric about expansionism was always directed at the Slavs. It's questionable whether Hitler would have attacked France when he did but for the opposition of France and Great Britain to the annexation of Poland.
So, there were very good reasons not to get involved. Some would argue that it would have been better to let Hitler destroy Stalin first.
I don't believe anybody realized until it was too late that Germany's economy, in particular foreign exchange, was so screwed up that the only way it could keep going was to steal money, hence the serial invasions, which gave them serial cash infusions.
German technology has always been very advanced but unfortunately Germany lacked essential commodities that could only be obtained through force or foreign exchange. Hitler screwed foreign investors too badly to have any foreign exchange. Remember Germany trying desperately to synthesize oil and rubber.
They had a similar problem during WWI, btw. That's why they invented fixation of nitrogen so they could make explosives, since they didn't have any natural source of it. |