B.
The Allies chose to appease Hitler and Nazi Germany prior to WWII strictly to avoid another conflict. The pain from the First World War was still felt by every nation it touched, and the Allied Powers desperately did not want to have another conflict like that. So they stood by and watched as Hitler expanded Germany’s reach, until he invaded Poland, a country which Britain and France had pledged military support to if Germany had invaded. That was the spark that woke the Allies up to Hitler’s belligerence and started the Second World War.