That Britain’s war guarantee to Poland was a monumental blunder,
...
By threatening war for Poland, Britain impelled Hitler to cut his deal with Stalin.
...
Had Britain not declared war, Hitler would have attacked an unprepared Stalin in 1940. The result might well have been the liberation of the Gulag and its 12 million souls, the eradication of Bolshevism in Russia and China, no Cold War, no Korea, and no Vietnam.
https://buchanan.org/blog/pjb-an-unnecessary-war-328