Between 1861 and 1940, approximately 275,000 Japanese immigrated to the United States, with the majority arriving between 1898 and 1924, when quotas were adopted that restricted Asian immigration. Assimilation and acceptance proved hard to come by for many of these Japanese immigrants, but following the attack of the Japanese on Pearl Harbor on December 7, 1941 their new lives in America truly fell apart, as the U.S. Congress and the President yielded to pressue to remove individuals of Japanese descent (whether issei, first generation of Japanese in the U.S., and nisei, U.S. born, second generation Japanese Americans) from the West Coast states. On February 19, 1942, President Franklin Delano Roosevelt issued Executive Order 9066 authorizing the exclusion - an order implemented by Congress on March 21, 1942 as Public Law 503.
During the next 6 months, more than 120,000 men, women and children were rounded up and transported to isolated, fenced and guarded relocation centers, commonly referred to as internment camps. Nearly 70,000 of these individuals of Japanese descent were American citizens by birth. Most lost their homes and property - and all lost their freedom and personal liberties - although they had done nothing wrong and no charges were ever made against them.
Records created during the relocation of "potentially dangerous persons" to ten relocation centers operated in Washington, Oregon and California by the War Relocation Authority during WWII can be obtained from the National Archives. They generally include little to help you trace the family back to Japan, but may include parents' names, correspondence and other items of interest, including previous adress, occupation, education, foreign residence, sex and marital status, year of birth, age and birthplace. The Internment Case Files, located in Group 210, Records of the War Relocation Authority, can be obtained by making a Freedom of Information Act request through the National Archives. They can also be accessed online through the National Archives Access to Archives Database. Once you find the record for a specific individual, you can search for records for other family members via the 5-digit "Individual Number" or "File Number." The members of one family usually have the 5-digit number in common, with a following letter denoting the position of the person within the family. Records relating to the compensation to Japanese Americans relocated during WWI for losses of real and personal property can also be searched online in Japanese Claims Act of July 2, 1948 Case Files (Record Group 60).
Separate from the Japanese American relocation program run by the War Relocation Authority, two additional programs were implemented by the United States to identify and imprison civilians considered a threat to the country during World War II. The first program, run by the Department of Justice, targeted German, Italian and Japanese nationals ("enemy" aliens) residing in the U.S. after the start of the war. Presidential Proclamations 2525, 2526 and 2527 were issued by President Franklin D. Roosevelt to authorize the FBI and other law enforcement agencies to detain suspected enemy aliens living in the United States - primarily individuals of German, Italian or Japanese ancestry. A secondary program, run by the Special War Problems Division of the State Department, offered Latin American countries the opportunity to send allegedly dangerous enemy aliens living in their country to the United States for internment (many of them citizens of the Latin American country from which they were taken). Over fifteen Latin American countries accepted the offer, sending over 6,600 individuals of German, Italian and Japanese ancestry to the U.S. for internment, along with many family members.
By the end of WWII, over 31,000 suspected enemy aliens and their family members had been interned for at least a time at enemy alien internment camps run by the Immigration and Naturalization Service. Many were paroled or released following an appearance before a local hearing board. Several thousand were repatriated to their native country, some voluntarily and others involuntarly. At the end of the war, internees no longer deemed "dangerous" were released, although it took until 1948 before the last internment camp was closed.
Records relating to the internment of World War II enemy aliens are located in several different record groups in the custody of the National Archives. The index to the WWII Alien Enemy Detention and Internment Case Files can be searched online in ARC (Archival Research Catalog).
The United States was not the only country to intern alien civilians during WWI and WWII. The Isle of Man was used as a base for Alien Civilian Internment Camps during both wars. The National Archives of Australia holds records of internment camps and the enemy aliens held there during both World War I and World War II. Canada held over 8500 "enemy aliens" in internment camps, of which over 5,000 were Ukranians, in the period following the outbreak of WWI, and obliged an additional 80,000 individuals to register as "enemy aliens." Similar internment camps existed in France, Germany and other countries around the world.