How ever could three nations, with only 1% of earth's land territory and 10% of world population, hold the rest of us at bay, for six long years ?

Neutrality.

The neutrality of the schoolyard bystander - the Nordic disease - which by 1939 had infected almost the whole world.

Accept as a given fact that a Grade Six bully (Hitler) can't really beat the crap out of dozens of primary school kids (Poland et al), not all by themselves, not unless the rest of the schoolyard stands around with their hands in their pockets, agnostic as the results of the 'fight'.

Because in the Age of Human-Only Progress, it was seen as inevitable that the biggest and toughest humans would beat up the smallest of humanity, as it was that they beat up insects and bacteria.

Might was just bound to be right, in the struggle of the survival of the fittest.

Regrettable but true.

Our great great grandparents sighed for a moment, just a moment, over the very sad fate of the Belgians or the Canadian Indians, and then got on with life.....