Naturalized? What does that mean?

A person who was born in another country and comes to live in the United States, is not a citizen until he has lived among us a certain time; and then, has taken a solemn oath to obey the Constitution. He is then admitted as a citizen of our republic. This process is called naturalization; and once naturalized, he is allowed full citizen rights including the choosing of rulers, just as if he had been born among us.