Immigration is when a person comes to a new country to settle. A long time ago, people did it a lot. They moved to get away from religious enforcements, to make new economic opportunities and to get away from poverty. It is a way to make their life better. There was a lot of space in the U.S.A so it was easy to move in and grow crops. Most of the immigrates passed through Ellis Island, New York. 25% of modern Americans can trace back their ancestors to Ellis Island! Even when you go to a country just for vacation, you still have to pass through immigration. Nowadays, people usually move for jobs.
That is what I learned from the Brain pop movie.