Background
The USS Arizona sinking during the Attack on Pearl Harbor - Image Source
While the attack on Pearl Harbor and hysteria surrounding the war were catalysts for the internment of people of Japanese descent, there were also many other events leading up to the camps.
Timeline
1790: Naturalization Act of 1790 – Limited naturalization to those who were White and had “good character” ( Wikipedia).
1873: Naturalization Act of 1790 is amended to include “persons of African nativity or descent” – which along with the initial Act prevented people who did not meet those descriptors from gaining citizenship (Densho).
1882: Chinese Exclusion Act is passed, barring Chinese immigration to the United States until 1943 ( Wikipedia ).
1905: “The Asiatic Exclusion Act is formed in San Francisco” (Densho).
1908: Gentlemen's Agreement - Japan agrees to deny passports for anyone migrating to the United States and recognize that the United States can deny people originally from Japan from entering the United States ( History.com ).
1913: The Alien Land Law is passed in California, preventing anyone that cannot achieve citizenship from owning land(Densho).
1924: Immigration Act of 1924 is enacted, ending immigration from Japan to the United States (Densho).
November 1941: The Munson Report - an intelligence report ordered by President Roosevelt, concluded that the people of Japanese descent on the West Coast pose no threat to national security (Digital History).
December 7, 1941: Pearl Harbor is attacked and the FBI arrests Japanese immigrant "community leaders" ( Densho ).
Throughout December 1941: The FBI searches homes and confiscates anything deemed a threat to the community ( Densho ).
February 19, 1942: President Roosevelt enacts Executive Order 9066, putting into motion the internment of people of Japanese descent ( Densho ).
This timeline is based off of Densho's Timeline .