The United States has always had immigrants. The Western Hemisphere was the last place to be settled by man.
We are not based on blood, but ideas. Come here, work hard, be a pioneer for your family and hack out your place in the wilderness.
You have to have an invite though. Allow me to break this down on a neighborhood level. I invite you to my home, you don't just walk in and squat. I would not walk in and trespass in your home.