“Why did the tanks roll? Because Poland refused to negotiate over Danzig, a Baltic port of 350,000 that was 95 percent German and had been taken from Germany...”
Yeah, that was it exactly, and Hitler was such a trustworthy guy. /s
[He (Hitler) gave his word that he would respect the Locarno Treaty; he broke it. He gave his word that he neither wished nor intended to annex Austria; he broke it. He declared that he would not incorporate the Czechs in the Reich; he did so. He gave his word after Munich that he had no further territorial demands in Europe; he broke it. He gave his word that he wanted no Polish provinces; he broke it. He has sworn to you for years that he was the mortal enemy of Bolshevism; he is now its ally. Can you wonder his word is, for us, not worth the paper it is written on? ]
http://www.yale.edu/lawweb/avalon/wwii/bluebook/blbk144.htm
Kennedy negotiated with Kruschev in the Cuban missile crisis, and thank God. The best alternative to a negotiated settlement was either Russian missiles in Cuba, or nuclear war then and there. It turned out that there was a better alternative for both parties, which was achieved through negotiation.
Now you could argue that for England and the US, Poland's implacability was the best outcome because we had early warning of Hitlers intentions, he got somewhat bogged down in other things giving us time to prepare and we did not have to deal with creeping incrementalism, against which we would never have been prepared. But that does not mean it was necessarily best for the Poles who got the worst outcome they could have gotten.