What was the perceived threat that led to the internment of Japanese-Americans in the late 1930s?

I saw a documentary about FDR's administration and how it implemented its war plans in the 1930s. There was a lot of anti-Japanese sentiment in the country at the time, culminating in mass internment camps and the forced emigration of Japanese-Americans during the war. How widespread was anti-Japanese sentiment at the time, and what was the perceived threat that the administration considered so serious as to warrant internment camps?<br><br>Also, was there any evidence that Japanese-Americans were being conscripted into the Imperial Japanese Army at the time, or was this just a preposterous conspiracy theory upheld by the government?