U.S. citizens can give up their citizenship voluntarily by becoming the naturalized citizen of another country. There are a few ways to do this, such as running for office or serving in the military in a new nation. An individual’s citizenship can also be stripped if he commits an act of treason.
The 14th Amendment to the Constitution declares that a person is a citizen of the United States if he is "born or naturalized in the United States and subject to the jurisdiction thereof." Many people from all over the world choose to become U.S. citizens every year. However, citizenship isn't always permanent. While exceedingly rare, it is possible for individuals to lose or renounce their American citizenship.
TL;DR (Too Long; Didn't Read)
U.S. citizens can give up their citizenship voluntarily by becoming a naturalized citizen of another country. They can also be stripped of citizenship if it was wrongfully gained.
Lying on Your Application
If you are a foreign-born resident, you must complete an application process to become citizens of the United States. You must tell the complete truth on your application. Any deliberate lie, whether you are telling a falsehood or withholding the truth, can disqualify you from citizenship. For example, among other criteria, you must have lived in the United States for five continuous years before becoming a citizen. If you lie about your term of residency and the government finds out, your citizenship will be disqualified because you never should have been a citizen in the first place.
Owing Allegiance to Another Country
You cannot lose citizenship simply by living abroad for a long time. You can, however, be stripped of citizenship if the government feels that you have abandoned your U.S. residence. This happens if you demonstrate your voluntary allegiance to another country. For example, you might become a naturalized citizen of another country with the intent of renouncing U.S. citizenship. You could also lose your citizenship by swearing an oath of allegiance to another country, such as if you are working for the government of a foreign nation or voluntarily serving in the military of a foreign country if that country is at war with the United States.
This does not mean you cannot be a citizen of the United States and also a citizen of another nation; you can. This is known as dual citizenship. Neither the federal government nor state governments keep records of how many US citizens hold dual citizenship, so there is no way to know how many Americans currently hold citizenship in multiple nations.
Marrying a foreign national or otherwise becoming a dual citizen is not the same as swearing allegiance to another country. An American citizen should be concerned about losing his U.S. citizenship via allegiance to another nation only if he runs for government office in the other country, serves in its military or intentionally becomes a citizen of the new nation without going through the proper channel to preserve his U.S. citizenship.
Article III, Section 3 of the U.S. Constitution defines treason as "levying war" against the United States or giving "aid and comfort" to the enemies of the United States. A person must confess in court to the crime or be convicted based on the testimony of two eyewitnesses. Treason includes making war or helping a foreign power make war against the United States and also includes trying to overthrow the U.S. government or Constitution. Committing treason is a sure-fire way to lose your citizenship and serve time in prison.
A final way to lose your citizenship is to give it up. Giving up your U.S. citizenship is almost always a permanent decision, unless you renounced your citizenship as a minor and decide within six months of turning 18 that you wish to have it reinstated. To renounce your citizenship, you must first travel to a foreign country. You must stand before a U.S. diplomatic official at a U.S. embassy or consulate and sign an oath renouncing your citizenship. Upon doing so, you will lose all the rights and privileges of citizenship in the United States.
After a recent growth of renunciations over the past few years, the number fell in 2017 and 2018. Many Americans who choose to renounce their citizenship do so to avoid paying taxes to the United States government. In 2010, the Foreign Account Tax Compliance Act (FATCA) rendered certain U.S. citizen-held foreign assets subject to federal taxes. This drove up the number of renunciations in the years following its passage. Perhaps one reason for the drop in renunciations is the process' prohibitive cost: $2,350. Although the official number of Americans renouncing their citizenship has dropped, there are likely far more who have abandoned the country and their citizenship without "officially" doing so.
- Illinois Legal Aid: Can You Lose Your Citizenship?; John Roska; April 2008
- U.S. Constitution Online: Constitutional Topic: Citizenship
- U.S. Department of State: Renunciation of U.S. Nationality Abroad
- Nolo: Can a Naturalized U.S. Citizen Lose Citizenship by Living in Another Country?
- Forbes: Fewer Americans Renounce Citizenship, but Taxes Still Drive Them