Answer:
Britain and France were willing to go to war over Poland because they had issued a guarantee to defend Poland's independence in March 1939. When Germany invaded Poland in September 1939, Britain and France declared war on Germany. Hitler had boasted that he had overcome the allies and thought that they wouldn't honor their guarantee of supporting Poland. The invasion of Poland triggered World War II, and Britain and France saw it as a threat to their own security. Despite their efforts to avoid war with Germany in the 1930s, the rapid defeat of Poland left them with no choice but to fight.