1938 vs. 1940 (2018)

I’d argue this was an advantage to Britain, not a disadvantage. Many of Britain’s ‘allies’ did as they were told and while theoretically had control of their troops destiny, actually did not.

Having supplies and manpower that could be built up and trained with little or zero threat of attack was very helpful.

“ On 10 November, knowing that El Alamein was a victory, he delivered one of his most memorable war speeches to the Lord Mayor's Luncheon at the Mansion House in London, in response to the Allied victory at El Alamein: "This is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.” From: https://en.m.wikipedia.org/wiki/Winston_Churchill#%22We_shal...

Speech here:

http://www.churchill-society-london.org.uk/EndoBegn.html

Except that's not how that went down at all. The Lend-Lease[0] policy was in place long before Pearl Harbor or the German declaration. What's more, Roosevelt strongly supported the Allies even before that.

[0] https://en.wikipedia.org/wiki/Lend-Lease

First break: in 1938 when Hitler was essentially gifted the Sudetenland by the Munich accords and by the inaction in an absurdly limp response from the Czech government. This particular region of Czechoslovakia was deeply protected by heavy military defenses and these in turn were backed up by a strong army run by a country that was (though it may seem a bit strange today) at the time one of the more robust and sophisticated industrial powers in Europe. Had the Czechoslovak government simply said "No, if you want it, you'll have to fight for it", Hitler's army would have likely suffered catastrophic losses invading the Sudeten region in 1938 and its entire later drive to conquest would have been ruined before it even really began. Instead, Beneš and Prime Minister Milan Hodža caved to pressure from Chamberlin and from Hitler as well, and lost their single best chunk of protective territory (not to mention the sheer morale loss that this entailed. From then, it was a simple thing to swallow the rest of Czechoslovakia in early 1939, further reinforcing the German war drive and industrial power. Had Hitler attempted to actually fight for the Sudetenland in 1938, his own generals knew that the Wehrmacht was still completely unfit for such an undertaking and they believed this to the point of being on the verge of a military coup attempt had it come to war. This was all (for Hitler) very luckily nullified by the completely counterproductive Munich agreement. Hitler came out of that looking like a political genius when in reality he was a frustrated fool who had desperately wanted war over the Sudeten region instead of diplomatic victory, despite it being a terribly bad idea.

Next, the lucky break of 1939: Yes, the German army was superbly equipped and armed by September of that year, but it was materially and numerically inferior to that of the French forces. Thus, when Hitler sent the vast majority of his forces into Poland in September, the only thing protecting Germany in the west was a thin screen of scant divisions along the border with France. Had France actually had the drive and political will to take its declaration of war in defense of Poland seriously and energetically, it could have mobilized fully and sent the full force of 40 divisions that the country's already prepared, ready, fully deployable "Saar Offensive" plan called for into the heart of western Germany. Doing this while Hitler was busy with Poland, in mid September would have been a catastrophe for the Germans, and would have completely ruined later plans to invade France. Instead, the French only advanced 30 divisions TO the Saar border, did essentially nothing more, and shortly afterwards, once the Polish campaign was over, Germany quickly reinforced this region with its own offensive action in October, 1939, causing the French to pull back completely. What an enormously wasted opportunity for boosting morale and war footing ahead of the game and crushing obvious future German aggression.