Following the attack on Pearl Harbor, President Roosevelt had very limited options and was compelled to declare war on Japan. As per the US Constitution, formal declaration of war requires approval from Congress. In order to obtain this approval, President Roosevelt delivered a compelling address to a joint session of Congress on December 8, 1941 giving one of the most significant speeches in American history. The speech began with the famous phrase, “December 7, 1941, a date which will live in infamy” and proceeded to make a persuasive case for declaring war on the Imperial Government of Japan. The speech proved to be a political success for President Roosevelt, as it not only rallied public support for the war effort but also solidified his leadership during a critical time. Furthermore, the speech achieved unanimous approval from the Senate, marking the official entry of the US into World War II. 

Following the attack on Pearl Harbor and President Roosevelt’s speech to Congress, the US proceeded to draft a formal declaration of war against the Imperial Government of Japan. This declaration marked the country's official entry into the global conflict known as World War II. The decision to enter the war triggered an escalation with other major global powers such as Germany and Italy, who declared war on the US three days later. For the allied forces, the entrance of the US in the war represented a major turning point as it meant that the world's largest economy and military would be formally involved in the war effort against the Axis powers. As a result of the war's continuation in Europe and the Pacific for another four years after the US declared war, nearly 420,000 Americans lost their lives. Nonetheless, the American victory and sacrifice represented a critical turning point in world history and strengthened America's position as the world’s leading global superpower.