They were considered traitors because of the Japanese attack on Pearl Harbor. The government became worried that citizens of Japanese ancestry would act as spies or saboteurs or otherwise pose threats like espionage against America. At the time, nearly 120,000 people fell into this category. Around two-thirds of that number were full-fledged citizens (born and raised here) of the United States. But, anti-japanese propoganda that caused fear and suspicion among the public encouraged the Roosevelt administration to forcibly send them away from their homes (across the country) to the internment camps.
