Pearl Harbor attack, when the FBI rounded up almost 1,300 Japanese American community leaders, seized their assets, and sent them off to inland facilities. Later entire families, including children, old people, and the disabled, were forced to pack what they could carry and move to temporary holding camps that were often converted stables and livestock fairgrounds. From there they were imprisoned in other heavily guarded facilities.

One of the men primarily responsible for the internment camps was the leader of the Western Defense Command, Lt. General John L. DeWitt. He came up with the idea of establishing military zones on the West Coast. To strengthen his arguments, he created a falsified report claiming that Japanese Americans had been guilty of sabotage. DeWitt proposed the internment idea to Attorney General Francis Biddle and Secretary of War Henry Stimson. DeWitt's initial plan also called for the roundup of German and Italian Americans, but the internment of white people of European ancestry proved to be less popular in high places. During Congressional hearings, high-profile politicians such as Earl Warren, who eventually became Chief Justice of the Supreme Court, backed the plan of interning Japanese Americans. Japanese Americans lived in difficult conditions and were treated as prisoners. Some were even shot when they inadvertently got too close to fence lines.

The internment of Japanese Americans is now considered a horrendous episode in American history. In 1976, President Gerald Ford signed legislation that prohibited the Executive Branch from ever again issuing similar orders. In 1988, President Ronald Reagan apologized on behalf of the US government and authorized payment of reparations to internees and their descendants.

We see, then, that the main causes of the Japanese internment during World War II were greed, paranoia, racism, and an overreaction to the Japanese attack on Pearl Harbor.

During World War II, the United States set up internment camps for Japanese-Americans. There were reasons for doing this, although we later regretted our actions and formally apologized to them. We also made restitution to those Japanese-Americans who were still surviving.

One reason for setting up these camps was a fear that Japanese-Americans would aid the Japanese during World War II. Since we were fighting Japan, people worried that the loyalty of the Japanese-Americans would be with Japan and not with the United States. It turned out that this fear was unfounded because no Japanese-Americans were convicted of aiding Japan during World War II.

Another reason for setting up these camps was that many Americans resented the economic success of the Japanese-Americans. There were fears that the Japanese-Americans were taking jobs and economic opportunities away from the American people. World War II gave people an opportunity to remove the Japanese-Americans from the economic picture. This would create more opportunities for Americans. Americans could take over the jobs the Japanese-Americans were doing and run the businesses the Japanese-Americans were operating. Many times this economic fear was used to cover up the anti-immigrant feelings many Americans had toward the Japanese, especially for those Americans who lived near the west coast.

The United States government formally apologized to the Japanese-Americans in 1988. Each surviving Japanese-American was offered $20,000 as a form of restitution for our government's actions during World War II.

Internment of Japanese Americans was caused by a number of factors which include as mentioned by Pohnpei397:

• Racism
• War Hysteria
• Fear and suspicion

There was profound racism against the American Japanese both from the society and some government policies. White farmers in the West Coast were highly prejudicial against their Japanese counterparts and the attack on Pearl Harbor offered them an opportunity to condemn and take away the farms owned by people of Japanese origin. Such groups instigated and fully supported the internment camps to enable them reach their objectives.

The government considered sabotage and espionage as activities that led to the success of the attack. People of Japanese decent were collectively viewed as supporters of the attack considering the first generation of Japanese settlers were not American citizens and owed allegiance to their mother country.

War hysteria led to growing fear propagated by provocative journalism among the society in general. This led to increasing pressure on the government to detain people of Japanese decent regardless of their existent or nonexistent role in the attack.

The internment of people of Japanese descent in America during WWII was caused by two things.

First, it was caused by a very understandable fear for the security of the country.  Japan had managed to pull off the attack on Pearl Harbor, which no one had thought was possible.  The idea that they might attack the West Coast while the US military was still weak was not absurd.

Second, it was caused by racism.  There was still a strong strand of racism in American society at this time.  For example, Asians were not allowed to become naturalized citizens, which is why the Issei were not citizens.  This racism led Americans to be willing to intern all people of Japanese descent without trying to determine individual guilt or innocence.

During World War II, the United States government forced Japanese-Americans that were living on or near the west coast to be relocated to internment camps at various sites in the country. The main reason given for this was that the government considered them to be a threat to our war effort. They were afraid these people would help Japan and would sabotage American military efforts against Japan. Another factor that played into this was the discrimination that existed toward Japanese-Americans. Some Americans were jealous of the economic success of the Japanese-Americans and feared they were taking jobs away from other Americans.

As a result of this forced relocation, Japanese-Americans were affected in many ways. Many Japanese-Americans had to sell everything they had, including their homes and businesses. They had no idea what would happen to their homes and businesses while they were gone. The conditions in the camps were not good. Overcrowding and disease were common. Some people died in the camps. In 1988, the government formally apologized to the Japanese-Americans and awarded each living survivor $20,000. The Japanese-Americans were loyal to our country and aided the war effort of the United States. The internment of Japanese-Americans during World War II is one example of how the United States has poorly treated people from different countries at various times throughout our history.

Mostly fear that there were among the Japanese population in the USA, people who would help Japan in its war against USA; there was fear in America of a Japanese invasion of California.

Another reason held by a few people was fear that mobs of Americans might attack Japanese residents in USA, and so, these few people thought, the Japanese needed to be put where they could be protected.

During World War I, there had been a lot of fear in America of German-Americans, but other Americans saw that they were loyal and by the time of World War II, were not so worried about them as about the Japanese-Americans.  Also the Japanese looked different so that there was more fear of them (that is probably racist) and they were more likely to become a target of mob action if left unprotected, since it was easy to identify them by sight alone.

American fear and suspicion caused the internment of Japanese Americans during the Second World War.  Operating out of a position of fear, paranoia, and skepticism, President Roosevelt signed an internment order that relocated all Japanese Americans and Japanese people in camps on the West Coast of the United States.  The fear was that the Japanese were plotting another Pearl Harbor style of surprise attack and that Japanese spies, or those who could operate as spies, needed to be rounded up and given a loyalty oath to the nation.  The camps in which they were relocated lacked effective medical care, and were situated in the desert, subject to extremely hot temperatures.  The stress of being relocated and living a life in camps had adverse physical and psychological effects on many.  At the same time, the consequence of the internment was that the court concluded that many of the Constitutional Rights of the detainees had been violated, under the Habeas Corpus clause of the Constitution.  At the same time, I would suggest that the internment of Japanese Americans displayed a level of contradictory behavior in American policy and its ideals.  A nation predicated upon individual freedom and liberty was denying it to a group, about 2/3 of whom were Americans.  Finally, another consequence was that while America stood strong in its commitment to European and Japanese fascism, it was engaging in practices that were perilously close to this foreign brand of repression within its own borders.

The cause of the internment of the Japanese Americans was suspicion and fear of having the US war effort hurt.  The American authorities believed that Japanese Americans were likely to remain loyal to Japan.  This made the authorities think that the Japanese Americans would be likely to spy for or otherwise help the Japanese against America.

You can argue that racism was a factor since something like 110,000 Japanese Americans were interned whereas only about 1100 German Americans were interned.  and The Germans were picked individually based on things they had done where the Japanese were interned based solely on ethnicity.

As for consequences, there were not really any for the nation as a whole.  For the people who were interned, there were major consequences as many of them lost a lot of property when they were interned.