That Hitler, Stalin and Tojo invaded small country after small country after small country while the world's peoples did basically nothing, unless and until their own nation was under direct attack, is a fact.
A fact as known to the people of 1940 as it is to us in 2015.
But a fact must first fit into a generally accepted system of explanation to be fully 'understood' : call that system of explanation a global worldview, hegemony, ideology, ethos, sentiment --- what have you.
Modern sentiment (or lack thereof) followed upon Modern Science
I believe most of the educated middle class during the Modern Era did greatly 'regret' that the small and the weak were nothing but road kill beneath the advancing wheels of the biggest civilizations.
But they regretted the small and the weak's demise with a faint shrug of their shoulders --- they firmly believed that the 'Laws of Nature', as demonstrated by modern Science, simply meant the demise of the small was inevitable and could, at best, be only delayed but never stopped.
Their demonstrated lack of 'sentiment' towards WWII's weak and the small was at least consistent with their existing scientific beliefs.
Postmodern sentiment followed postmodern science
By contrast, in the Fall of 1940, Dr Martin Henry Dawson felt his own scientific research indicated precisely the reverse view of the 'Laws of Nature'.
He felt that in History's long run, the small and the weak tended to vanquish the big and the complex.
The tiny bacteria, for instance, surviving all over the world for four billion years and counting versus the huge dinosaurs : where are they today ?
Dawson's willingness to give up his own life, that Fall of 1940, to see that wartime penicillin was extended to all those dying for lack of it, is usually explained as the result of his great sentiment towards 'the plight' of the weak and the small.
But it could also be argued - it is so argued, at least by me - that his sentiment towards the weak and the small followed precisely his growing (postmodern) scientific understanding of the resilience of the weak and the small ...