In September 1939, Britain (and France) did reluctantly go to war against Germany when it invaded Poland --- but hardly to protect this smaller, weaker nation from being being swallowed up by a bigger neighbour.
They basically sat on their hands while Germany, Slovakia and Russia invaded it and then divided it up.
Right to the end of the war and beyond, Britain (and now America) secretly horse-traded away the freedom of small nations; yes including the soon to be liberated Poland.