Chinese immigrants first started coming to the US in the 1850s to work on the railroads. Though they were critical to the construction of the railroads, the Chinese men who immigrated were subjected to discriminatory laws in California (where they lived, for the most part). The Chinese Exclusion Act of 1882 is (to date) the only federal law to restrict immigration based on race, and it largely kept Chinese immigrants out of the country until the Magnuson Act in 1943. During World War II, Japanese Americans on the West Coast (where most of them lived) were interned in inland camps, and many lost their homes and businesses as a result.

There were several reasons why Asian immigrants were treated differently than Europeans. They were linguistically different than other groups, and they looked different from Europeans. In addition, they were seen as threatening and as taking jobs away from white Americans. In part, jealousy and greed were behind the internment of Japanese Americans during World War II, as many Japanese Americans owned and operated lucrative farms and other businesses. Their success, in part, propelled the public to move to intern them during the war, though at the time, the reason given by the government was that Japanese Americans were likely to aid the Japanese military in an invasion of the West Coast.

While essentially all immigrants had a hard time when they came to the United States during this time, Asian immigrants had it worse than European immigrants.  This was largely because they were seen as more alien to white Americans.

The different treatment of Asians began before the 20th century.  There was, for example, the Chinese Exclusion Act of 1882, which banned most Chinese immigration for 10 years.  The ban on Chinese immigrants was made permanent in 1904.

Asians were also discriminated against more overtly than Europeans.  San Francisco, for example, had segregated schools for Asians in the early 20th century.  The naturalization of Asian immigrants was also illegal.  This is why, for example, the first generation Japanese immigrants who were in the US during WWII were not American citizens while their children were.

All immigrant groups faced problems in America.  But the problems were worse for Asians because of their race.