What major event took place that put "the wheels in motion" for Presidential Executive Order 9066?

Following the attack on Pearl Harbor on December 7th, 1941 the United States government was focused on establishing security and control of its territories, in hopes of avoiding additional attacks. One such measure comes from the President Executive Order 9066 enacted by President Franklin D. Roosevelt allowing the government and military to declare any US territory a military zone and the removal of all civilian populations in the area. This executive order allowed for the resettlement Japanese Americans into internment camps.