Chamberlain was called an appeaser. At the time it was considered a compliment. One could argue that Hitler may have been deterred from invading countries if the rest of Europe (and the US) had been stood up to him. IMO thats nonsense. He was a nutter intent on domination. Chamberlain (maybe not wholly intentionally) managed to win some precious time in order to build up the UK defences (somewhat anyway) . True, this was at the expense of 'giving in' to Hitler over Czechoslovakia.
I'm not sure that the UK had promised Poland that it would be defended against an attack by the Soviets??? Yes the UK had an agreement to fight Germany if it attacked Poland .... and it kept its word.
As for after WW2 when the Soviets took control of Poland ... I'd suggest its a little naive to say the UK and France should have gone to war with the USSR. Their economies were rock bottom, the USSR were (or close to) being a nuclear power and the USA wouldnt have (I'm sure) given them any support.
