What are reasons for immigration into the United States?

Many. From marriage, employment, education (College aka University), among many others. And, in the case of illegal immigrants, try to earn more money than in their home countries and live relatively better. Some go back to their countries after some time; some never do and live the rest of their lives here. Those who stay here the rest of their lives ussually get their green cards when their US born children reach 21 years old or if an amnesty shows up. Religious freedom and for a better life,War, better jobs