The United States is a country of immigrants — people who come to one country from another country, in hopes of having a better life. An inscription on the base of the Statue of Liberty welcomes new immigrants: "Give me your tired, your poor, / Your huddled masses yearning to breathe free..."
Don't confuse the words immigrant and emigrant. If you come to a country, you are an immigrant and you emigrate from somewhere else. Ireland has many emigrants to America; America has many immigrants from Ireland. If your parents were immigrants to the United States, but you were born here, you are a citizen automatically.