The Statue of Liberty, France's gift to the United States, was originally viewed as a tribute to the end of slavery. But poet Emma Lazarus reimagined Lady Liberty as a "mother of exiles," welcoming immigrants to the shores of America. Correspondent Mo Rocca looks at how the opening of Ellis Island, the end of restrictive immigration quotas, and John F. Kennedy's evocation of the United States as "a nation of immigrants" transformed our country, in this entry in the "Sunday Morning" series "These United States."