A lot of people underestimated the Red Army. Remember, in the 1920s they'd been fought to a standstill by the Poles, they're surrogate side had just lost in the Spanish Civil War and Stalin's purge had decimated their USSR's military.
Poland had done a masterful job of inflating it's military capabilities and, also remember nobody really thought all those masses of tanks the Germans and Soviets had were really going to make a difference.
In retrospect, it seems obvious Poland was doomed. But it's also true that Poland's defensive plan played right into the German's hands, and nobody expected the USSR to stab them in the back.
You're right about Poland, but that was a long time ago. (Pilduski was then POL's leader?) And Spanish Republic was rather lonely, can't really compare USSR's aid to ITA and GER's massive ones. And we all know GBR blatantly favored Franco, such as Churchill, sea lords..
Did Europe know about the massive military purge then? 1937 or something, right?
Well, CZE was definitely better than POL in terms of military strength, and moreover POL didn't have natural fortress to fall back to. And cavalry charge against machine guns was already proven futile in the American Civil War.
And Chamberlain was not even enthusiastic about providing military funds for POL..make up your mind, Neville
(well, I guess he believed Hitler to the end
He liked Germany best, at least more than USSR or USA
And about stabbing in the back, why not? History proves it, POL was stubbornly refusing the triple alliance, Chamberlain was not really going for it either, what alternative did Stalin have? Stalin was a tough, tough negotiator too, he bought time (against GER's invasion)
But in the end he also was naive about Hitler, he didn't think GER will invade so soon, so was supplying them with natural resources right into the date of Barbarossa