Read “world war 2 behind closed doors” by laurence rees
There was a secret part in the treaty between the french, british and poles which the brits and the french promised military assistance against a German attack not a Soviet attack and remember they did not help in the war between the poles in the soviets in late 1910’s and early 1920’s but instead suggested the curzon line (which the Molotov-Ribbentrop line basicly followed)
Also the soviets at Tehran were more interested in soviet post war borders than they were in actually winning the war and remember in 1943 this was not a certainty. They wanted to keep there pre 1941 gains.
This is just a brief overview of some othe parts of the book I suggest you read it. It is very good.
The brits and the french could have attacked the siegfried line before the germans finished it and probably would have been succesful and because they did not co-operate with the Belgium people (I don’t know the correct word) and the dutch because the later two did not want to appear co-operating with the allies because at that time they were neutral. The Germans had a brilliant strategy in attacking (the aaa territory North West Europe) and then following nit up with the tank drive through the ardennes they cut of the Elite French and British troops from the rest of the army. They shouldn’t have allowed Dunkirk and should have forced the British and French into the sea and this would come back to haunt them.
