Understand the mainland Chinese thinking in this video (youtube.com)
Immigrants won't go fight their own people in a war, generally. They wouldn't enlist in their home country's army either, in a lot of cases, even if they had the opportunity to do so.
Perhaps even more true of migrants into the US, because the main reason to go to the US is economic. Many people in the countries I visit now say they would go to the US, only to make money and come back. There's no real reason they want to be there other than money and also prosperity that they see in movies, like movies set in New York.