Citizenship of the United States
A person who is considered a citizen by more than one nation has "dual citizenship". It is possible for a United States citizen to have dual citizenship; this can be achieved in various ways, such as by birth in the United States to a parent who is a citizen of a foreign country (or in certain circumstances the foreign nationality may be transmitted even by a grandparent) by birth in another country to a parent(s) who is/are a United States citizen/s, or by having parents who are citizens of different countries. Anyone who becomes a naturalized U.S. citizen is required to renounce any prior "allegiance" to other countries during the naturalization ceremony; however, this renunciation of allegiance renunciation of citizenship to those countries.
Family reunification
Citizens and permanent residents of the United States may sponsor relatives for immigration to the United States in a variety of ways. Citizens of any age may sponsor their spouses and their children, but only citizens who have reached the age of 21 may sponsor siblings and parents. (The Supreme Court decision "United States v. Windsor" ruled in 2013 that same-sex spouses must be treated the same as opposite-sex spouses.) Permanent residents may only sponsor spouses and unmarried children. The sponsor must demonstrate the capacity to support their relative financially at 125% of the poverty level.