How was immigrant labor beneficial to the United States?

The United States owes a lot to immigrant labor. Immigrants provided a lot of the unskilled labor which built this country. Irish and German immigrants helped make Henry Clay's American System thrive by building the necessary infrastructure such as the canal and railroad system. These immigrants came looking for work and they often took jobs for low wages that native-born Americans would take only as a last resort.
Even though anti-immigrant bias has been common since the country's inception, immigrants have been valuable in performing jobs that Americans needed. Chinese immigrants were quite successful in the gold fields of California—so successful that they were wrongfully accused of stealing claims and this was part of the reason why the nation passed the Chinese Exclusion Act in the 1880s, the first time the nation attempted to restrict the immigration of a specific group.
After the Civil War, thousands of immigrants came from Southern and Eastern Europe in order to work in the factories of the major metropolitan areas. This led to friction between the new immigrants and native-born Americans who feared for their jobs and their way of life as these new immigrants were slow to assimilate due to their settling in already-established immigrant communities. Immigrants also provided valuable skilled labor over the years as well, as most of America's early work on outer space would not have been possible without German rocket scientists.
Currently, the United States still needs immigrant labor. The H-1B visa program brings in skilled laborers from all over the world to work in fields such as IT and medicine. Undocumented workers are controversial; yet without them, much of the nation's manual labor would go undone. There would be virtually no one to harvest our food. Also, these workers contribute to the local economy by spending their wages in the US. While minimum wage floors have allowed the immigrants not to compete for lowered wages like they did in the 1800s, the plight of unskilled immigrant workers is still scary.