Expulsion refers to a subordinate group being forced, by a dominant group, to leave a certain area or country. As seen in the examples of the Trail of Tears and the Holocaust, expulsion can be a factor in genocide. However, it can also stand on its own as a destructive group interaction. Expulsion has often occurred historically with an ethnic or racial basis. In the United States, President Franklin D. Roosevelt issued Executive Order 9066 in 1942, after the Japanese government’s attack on Pearl Harbor. The Order authorized the establishment of internment camps for anyone with as little as one-eighth Japanese ancestry (i.e., one great-grandparent who was Japanese). Over 120,000 legal Japanese residents and Japanese U.S. citizens, many of them children, were held in these camps for up to four years, despite the fact that there was never any evidence of collusion or espionage. (In fact, many Japanese Americans continued to demonstrate their loyalty to the United States by serving in the U.S. military during the War.) In the 1990s, the U.S. executive branch issued a formal apology for this expulsion; reparation efforts continue today.