After whites of European descent what are the 2 largest ethnic groups in the United States?

Han Chinese is the largest, at between 1.2 and 1.4 billion. (Current population of China is 1.33 billion. Years ago I multiplied the pop of China by the percentage that was Han, and added in the number of Han Chinese from each country in the world. I used some kind of world factbook, forget which one offhand. At the time (maybe 15 years ago), the total number of Han Chinese in the world was about the same as the overall population of China.)

Hope this helps, or at least points you in the right direction for some number-crunching.