Britain had no choice, up to 1939, the belief was that Hitler just wanted to unite Germans.
But the real goal Hitler wanted was to make sure there would be no states to the East that would be allied with Britain and France, which in Hitler’s mind meant that Germany would be “surrounded”, and that’s why he occupied the rest of Czechoslovakia. Without the Sudetenland, Czechoslovakia was defenseless.
Hitler had held out hope that perhaps Poland, driven by their hatred of the Soviets, would ally with Germany.
But after seeing what the Germans did in Czechoslovakia, Poland was determined to not suffer Czechoslovakia’s fate, and even secured a part of the former Czechoslovakia that was mostly populated by Poles.
On top of that, Britain and France were determined that they weren’t going to repeat Munich ever again. They already had egg on their faces, as it is. So they made the deal to “guarantee” Poland’s safety (although they knew if the Germans attacked they could never hope to save Poland).
Hitler’s number one goal was to kill Jews. The second one was to concor the USSR.