Question

According to the first paragraph from the excerpts of the majority opinion, what did the U.S. government believe some Japanese Americans would do if they were allowed to remain free on the West Coast?

Answer 1

Good Morning!

The main fear of the United States of America with Japanese residents on the west coast was that these individuals would turn against the US as the country was in a strong war against Japan and Axis forces. This suspicion led many Japanese to be placed in concentration camps. They feared spies and attacks by these individuals, many of them who had already left their country for decades.
 
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Answer 2

You didn't give us the excerpts, but here's an explanation:

During World War II, Japanese Americans were held in relocation camps  because of the fear that they would give information to the Japanese or attack the U.S.

Suspicious of anyone of Japanese heritage, the government restricted the civil liberties of Japanese Americans.  In February, 1942, President Roosevelt issued Executive Order 9066, which allowed the Secretary of War to designate certain areas as military zones.  FDR's executive order set the stage for the relocation of Japanese-ancestry persons to internment camps.  By June of 1942, over 100,000 Japanese Americans were sent to such internment camps.