Say the word "concentration camp", and you instantly conjure images of Nazis, the Jewish Holocaust and basically bad stuff. However, there were concentration camps all over the world which served to "concentrate" individuals by a common trait. At the onset of WWII, the US had concentration camps for German, Italian and Japanese Americans. This became a dark chapter in our history because the people forced into those camps were American Citizens. By virtue of a Declaration of War, they were denied due process, deprived of liberty and property, and subjected to incarceration in often appalling conditions.
This disproportionately affected Japanese Americans. While some point to racism as the fundamental basis for this disparity, that charge ignores that Italians - considered non-whites by the racial theories of the day - were not subjected to this level of marginalization. So what lead to the large number of Japanese being interned? Enomoto Takeaki, for one.
During the latter part of the Meiji period in Japan, Enomoto Takeaki rode a wave of right-wing nationalism to prominence. One of the theories Takeaki promoted was that Japan would need to expand its territory in order to provide for the economic prosperity of the Japanese people. This was a popular theory at the time, but most Japanese groups (Genyosha in particularly) looked westeward at China, Korea and Siberia. Takeaki set up the "Colonial Association" which concentrated on the America's. At the time, poor Japanese were eager to go abroad to work for a few years, earn money and return to Japan. Takeaki saw this as an opportunity to establish colonies in the America's that would later become part of an expanded Japanese Empire. The program was wildly successful, and later became official government policy.
Japanese emigration and colonialism was a little too successful. Communities of Japanese immigrants (Issei) and their native born children (Nissei) concentrated in cities like San Franciso, Portland and Seattle. Their closed communities coupled with displacing native workers earned them the scorn and distrust of large swaths of American society. This is in stark contrast to German and Italian communities which were more open and worked to integrate into American culture. Within a decade, there was a tacit agreement between the US and Japan whereby Japan would not issue passports for laborers. That left the influx of "student laborers", who went to American schools while working as domestic servants. There was, of course, illegal immigration of Japanese from latin America, and eventually Congress acted to ban all Japanese immigration. This left sizable communities in the US which existed as "mini Japans", closed to outsiders and very much oriented towards the Emperor, and away from the US. Japanese were largely resented on the West Coast,.
When Pearl Harbor happened, there was no question of their Loyalty in the minds of the public. In fact, many politicians who supported public laws for the relocation of the Japanese felt they were actually acting to protect the Japanese-Americans from public backlash. Early in the internment, the US Navy distributed a questionnaire to men in the internment camps. One question asked if they serve in combat. Another asked them to forswear allegiance to the Emperor, and pledge allegiance to the United States. A large number of Japanese answered no to both these questions. The tragedy is that many answered no to the first question because of their Pacifist beliefs, while others answered no to the latter question because they felt they could not forswear an allegiance they didn't hold. Nevertheless, these "no-no's" were singled out with many going to labor camps.
Enter a bit of redemption from this period - Nissei who answered yes to both questions were afforded the opportunity to serve in the US Armed Forces. They formed the 442nd Infantry Regiment and fought in the European theater, becoming one of the most decorated units of the war with over 14,000 serving. They also suffered among the highest casualty rates. Their tremendous courage and bravery earned them great respect. In 1951, the movie "Go For Broke" dramatized their exploits.
While it's easy to look back and judge an era through the lens of our modern sensibilities, people have to remember that we too will be judged based on how we respond to our current circumstances based on the evolved sensibilities of future generations.