Answer:
Following the attack on Pearl Harbor on December 7, 1941, the United States formally and completely entered World War II. Although previously they were already supplying the allies, from this attack the armed forces fully mobilized, going to war with Japan on the Pacific front.
This attack was completely surprising for the American forces, who did not contemplate this maneuver on the part of Japan. After this attack, all Japanese became an enemy, and their descendants in the United States became suspected of being collaborators with the Tojo regime: the Japanese Americans were at that time a closed group of immigrants, who maintained many customs and roots with their ancestral land, with which many politicians could boast that they would support Japan even while on American soil.
From these events, a collective anti-Japanese hysteria was generated, leading to many of the commercial premises of these people on the West Coast being looted and burned. Later, as a national security measure (nowadays much criticized), President Roosevelt issued his Executive Order 9066, by which internment camps were created to hold the Japanese Americans until the end of the war.
