There were about 10,000 Italians and Germans interred in Montana during WW II. Japanese were interred during the same period of time on the west coast because they could watch troop and ship movements. We were at war and the military were given the leeway to determine what action was needed, and it was done. I am fairly sure Japanese were interred on the islands of Hawaii. It seems to be a fact that is commonly known, whether it is true or not.
In the Continental US over 100,000 persons of Japanese descent were interned ~ most of them consisting of American citizens.
The rationale you propose, watching troop movements, was not given at the time. In any case, by the time the US got into a serious war with the Japanese (toward the end of the war with Germany), almost all the Japanese Americans had been released from the camps.
The real reason for their internment was the ambition by wealthy and powerful interests in California in their property. Once you were in camp you couldn't work your land and pay your taxes. The State of California seized their land and sold it to rich people.
I personally know people who lost land now consisting of Wilshire Boulevard and everything on either side for the depth of 2 miles. This property is worth billions.
The one spy that Japan managed to lodge in our nuclear research program in Chicago was German.