How did the oath change many Japanese Americans' attitudes toward America?

The oath, presented to the Japanese-American citizens in the internment camp, incited strong anti-American feelings even in people who previously were loyal to the US.

We find this out in Chapter 11, when Jeanne describes the oath and how it causes her father and brother to fight. The conflict radiates throughout the camp, and Jeanne describes the oath as "the final goad that prodded many once-loyal citizens to turn militantly anti-American." She goes on to describe a severe escalation in anti-American sentiments throughout the camp and a sharp divisiveness about how they should respond to the oath.

If we look at what the oath was asking these people to do, we can understand how their fury rose up so suddenly. Consider how they've been uprooted from their homes and essentially imprisoned in these camps, all because they have Japanese ancestry. Now look at what the oath asked: "Are you willing to serve in the Armed Forces?" and "Will you swear unqualified allegiance to the United States of America?"

There is no good way to answer these questions. Saying "no" would get a citizen in trouble, possibly jailed or deported. Saying "yes" would send a citizen straight into the war, fighting against his homeland and for the country who had imprisoned him unfairly. There was no box on the form to check that stated "I prefer not to answer these questions," so the very act of requiring the oath to be filled out was an injustice. You can understand, then, why anti-government feelings were engendered so quickly and passionately because of this oath.