Chugalug2
We went to war in 1939 because there was no alternative, not because we were obliged by Treaty obligations
Surely we went to war because Germany had invaded Poland. We had after all on 25th August 1939 signed an "Agreement of Mutual Assistance" with Poland. This agreement contained promises of mutual military assistance between the nations in the event either was attacked by some "European country".
As Chamberlain said on 3rd September 1939: "
This morning the British Ambassador in Berlin handed the German Government a final note stating that unless we heard from them by 11.00 a.m. that they were prepared at once to withdraw their troops from Poland, a state of war would exist between us."