In February of 1942, President Roosevelt issued Executive Order 9066, calling for the internment of "enemy aliens." Interpretations of those words varied widely, but the officer in charge of the Pacific Coast, Lt. Gen. John Dewitt, had perhaps the most liberal definition. When talking about the internment of Italians in California, there seem to be two major questions. First is why were some Italians interned, and the second is how did this internment differ from that of the Japanese-Americans?
The answer to the first question has multiple answers. One of the key elements is that many Italian immigrants to California did not become American citizens. As Executive Order 9066 was race neutral in its language, this meant that German and Italian citizens were at risk for internment. While the Italian-American population of California had a long history of integrating itself with the larger California population, those who did not naturalize, and these were often illiterate, were also less likely to have shown evidence of integration into "American" society. On top of that, the vibrant memberships of Italian-American groups and schools, both Fascist and non-Fascist, led to a questioning of their loyalties.
The answer to the second question is easier. Unlike the Japanese-American experience, no American of Italian heritage was interned. That means that unlike the argument for Japanese-American internment, that blood would trump environment when it came to civic loyalty, the argument for interning Italians only applied to those who were still Italian citizens. On top of that, while many Italian immigrants were forced to register, fewer than 300 were actually interned. Due to pressure from political and business leaders, all of those interned of Italian heritage were released by Columbus Day of 1942. At the same time, many non-citizens were forced to leave their homes, as they were located in one of the 86 zones the government had determined were necessary for national security. This led to the famous argument that Joe DiMaggio's parents were not allowed to visit their own sons' seafood restaurant, because it was too close to the coast.