Final answer:
The Atlantic Charter, a post-war vision concept drawn by Roosevelt and Churchill emphasizing self-determination, self-government, and free trade, was the major influence for President Roosevelt to integrate the defense
Step-by-step explanation:
The incident that most convinced President Franklin D. Roosevelt to integrate the defense industries in 1941 was not the Attack on Pearl Harbor, The Zimmermann Telegram, or The Lend-Lease Act, but rather The Atlantic Charter.
Roosevelt entered World War II with a vision that U.S. would succeed Britain as the leader of Western capitalist democracies. The Atlantic Charter was a fundamental document that spelled out British and U.S. goals for a postwar world.
It insisted on the unconditional surrender of the Axis nations and promoted peace through the disarmament of aggressor nations. This vision motivated Roosevelt to reinforce the defenses of America during this tumultuous time.
During the war, Churchill requested a face-to-face meeting with Roosevelt, leading to the creation of the Atlantic Charter. This charter emphasized self-determination, self-government, and free trade, principles that embodied Roosevelt's vision for a post-war period
Learn more about Atlantic Charter