There is quite a bit of international law about this, from quite a while back. The article notes, "Then again, it is a country’s sovereign right to decide who to let in and who to keep out—and not all countries consider fairness a priority when it comes to immigration policy," and that is largely true. But countries have obligations to their citizens in how they relate to other countries, and some of those reciprocal obligations have been tested in international law. The Guatemala v. Lichtenstein case (the Nottebohm case)[1] decided by the International Court of Justice, the successor to the Permanent Court of International Justice first established under the League of Nations, decided in 1955 that international law can examine the naturalization law of nation-states when citizenship is asserted by a citizen as protection against the actions of another government. The facts in the Nottebohm case were that Mr. Nottebohm had been born in Germany in 1881 and was a German citizen by facts of birth. He lived in Guatemala from 1905 until 1943 without becoming a citizen of Guatemala, traveling to Germany and other places on business from time to time. In October 1939 (just after the beginning of hostilities in Europe in World War II), Nottebohm applied for citizenship in Lichtenstein, which granted him citizenship despite its usual requirement of three years of residence before citizenship. When Nottebohm tried to reenter Guatemala after a period of travel in 1943, Guatemala (which by then had declared war on Germany as part of World War II) did not allow him reentry, but rather interned him as an enemy alien and transferred him to Guatemala's ally, the United States. After the war, the government of Lichtenstein sued the government of Guatemala for not protecting its (Lichtenstein's) citizen. In its defense, Guatemala claimed that it owed no duty to Lichtenstein to protect Nottebohm as a friendly alien, because Nottebohm did not have sufficient genuine connection to Lichtenstein to be treated as a citizen of Lichtenstein. The international court agreed that despite the general rule that countries may decide their own laws of citizenship and immigration, when a person from one country asserts a right of citizenship against the action of another country, the citizenship relationship can be examined by principles of international law.<p>The bottom line for you and for me: if you buy citizenship somewhere, and then travel somewhere else, you may not enjoy consular protection or any other diplomatic representation from the country whose citizenship you bought and paid for. You may be treated as a person with the birth citizenship you started out with (or some other citizenship acquired along the way), rather than the citizenship you chose for yourself, if your connection with your new country is weak and exists on documents more than it exists in fact. So be careful how you shop for citizenship and think ahead before you travel internationally.<p>[1] <a href="http://www.worldlii.org/int/cases/ICJ/1955/1.html" rel="nofollow">http://www.worldlii.org/int/cases/ICJ/1955/1.html</a><p><a href="https://en.wikipedia.org/wiki/Nottebohm_case" rel="nofollow">https://en.wikipedia.org/wiki/Nottebohm_case</a>