It is very, very, very hard for us today in 2015 to put ourselves in the mental mindset of the old men running the world in 1939.
For they had grown up during the heady worldwide high tech industrial boom that began in the 1870s.
That boom was primarily led by the inventions of just two industrial giants, equal to each other in population and scientific knowledge : Germany and America.
For us today can only see that America is more than four times the population of Germany and still growing - while Germany is losing population fast.
But back then both were equal in population with forty million people each.
Those old - badly outdated - childhood memories of when Germany was still equal in population and technology to the USA continued to govern the emotions of the old men who ran the Allies WWII war effort.
They thus greatly overestimated Germany's demographic and industrial strength and gravely underestimated their own.
This led them to avoid an early conventional weapons-based ground assault on Germany using their overwhelmingly superior demographics in favour of a slower (big money but small manpower) air-led assault using supposedly superior and secret technology.
The war thus dragged on needlessly for six bloody years, 75 million died directly and indirectly as a result , Russia did the land assault (albeit badly) and so got most of Europe behind the Iron Curtain - leading to a further 50 years of the Cold War.
A tragedy on so many fronts ....