The central idea in Roosevelt's "Address to Congress Requesting a Declaration of War" is that the United States must enter World War II to defend democracy and freedom against the Axis powers. Roosevelt argues that the United States cannot remain neutral in the face of aggression and tyranny and that it has a duty to support its allies and protect the interests of the American people. He calls on Congress to declare war on Japan and its allies and to mobilize the nation's resources to fight and win the war. Roosevelt emphasizes the grave threat posed by the Axis powers and the need for swift and decisive action to ensure victory. He also highlights the sacrifices that will be required of the American people and the importance of working together to achieve a just and lasting peace. Overall, Roosevelt's speech presents a compelling case for the United States to join the fight against fascism and tyranny in defense of democracy and freedom.