Dual Citizenship is the status wherein one person holds citizenship within two countries. To an extent this represents a conflict of interests in that at any time two given nations may be at odds or at least some aspect of the myriad details of international politics may divide them. At the same time however, from a legal perspective dual citizenship is the natural result of different definitions of what constitutes citizenship in a world in which people can freely move between nations.
To better understand dual citizenship one much first understand how citizenship rules vary from nation to nation. In the United States one holds citizenship based on being born within the legal boundaries of the United States. In other nations, for instance Russia or Israel, anyone born to a female of these nationalities, regardless of where, is entitled to citizenship. This can become confusing. For instance if a child is born on a flight over a territory that adheres to birthright citizenship, the newly born child may not be able to return to the nation from which its parents come without a lot of paperwork; in some cases even while the parents might face deportation in trying to stay with their child.
Travel for dual citizens is also complex. In most nations it is not legal for its own citizens to travel on a passport issued by another nation. Further while someone may hold two citizenships if it can be proven they are a citizen of a given nation that nation may ignore the arrangements it has with the embassies and consulates of other nations meaning that unless the dual citizenship is legally on the grounds of the consulate or embassy of the other nation (which usually constitutes sovereign territory of the foreign nation) they may not be able to appeal to agreements between the two nations involved. In some instances, depending on the arrangements between the two party nations and their citizenship rules a citizen may even face deportation to another territory in which they hold citizenship.
Even in the case of renouncing citizenship dual status can occur. For instance a citizen born to a Russian mother within the territory of the United States can at the age of 18 renounce their Russian citizenship while taking an oath to U S Citizenship, however the Russian Federation would not accept such an oath unless it was made to a Russian representative on the territory of the Russian Federation. This scenario also enables many to gain dual citizenship by taking a citizenship oath on the territory of a foreign nation where they know that such an oath is not relevant to their native nation. Some nations even relax citizenship rules to gain support of citizens of an adjacent territory who have family in, or wish to travel within its borders. This can be used to affect political policies within the nation of the dual citizen who would potentially be biased in favor of policies that benefit the nation granting second citizenship.
Further Information on Dual Citizenship
US Laws Regarding Dual Nationality