@Jean France and UK entered war with Hitler, but it was war only on paper, or so called "phoney war" (https://en.wikipedia.org/wiki/Phoney_War
) - or to speak plainly, just a betrayal of the promises given earlier. In practice, the UK did nothing at all (I think they might have thrown some leaflets from planes, but that's it), and France moved a small number of troops into German territory, only to withdraw it after some fighting a couple weeks later. Other than that, both Polish allies did nothing to stop Hitler from his aggression, which led to Stalin atacking Poland (and Finland) shortly thereafter, and Hitler attacking Denmark, Norway, Benelux countries and France.
The disconnect from reality on French and UK side was so big that, when Polish authorities saw that German attack was imminent and decided to give an order for mass mobilization on August 29th, French and UK ambassadors together convinced the Poles not to do it, as it would be "escalating the conflict". Unfortunately, gullible Polish government listened to them, which led to a chaotic mobilization during first days of September, already under German fire.