There-in lies the "crux" of the issue surrounding multi-nationals, or dual nations. Another country can lawfully lay claim to that individual (who holds foreign citizenship, by birth or by choice), most notibly, when it comes to the issue of a military draft. This has been a concern since the founding of the country. Leo discussed just this issue, recently [1].
dual nations —> dual nationals
7 FAM 081: U.S. Policy on Dual Nationality:http://www.state.gov/documents/organization/86563.pdf(e)While recognizing the existence of dual nationality, the U.S. Government does not encourage it as a matter of policy because of the problems it may cause. Dual nationality may hamper efforts by the U.S. Government to provide diplomatic and consular protection to individuals overseas. When a U.S. citizen is in the other country of their dual nationality, that country has a predominant claim on the person.
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the U.S. Supreme Court has stated that dual nationality is a "status long recognized in the law" and that "a person may have and exercise rights of nationality in two countries and be subject to the responsibilities of both." See Kawakita v. United States, 343 U.S. 717 (1952).
And this...
US State Department Services Dual Nationalityhttp://travel.state.gov/travel/cis_pa_tw/cis/cis_1753.html... The U.S. Government recognizes that dual nationality exists but does not encourage it as a matter of policy because of the problems it may cause. Claims of other countries on dual national U.S. citizens may conflict with U.S. law, and dual nationality may limit U.S. Government efforts to assist citizens abroad. The country where a dual national is located generally has a stronger claim to that person's allegiance.
However, dual nationals owe allegiance to both the United States and the foreign country. They are required to obey the laws of both countries. Either country has the right to enforce its laws, particularly if the person later travels there...