• You passed naturalization in another country.
• You made a formal renunciation of US nationality. That is, you have sent a written confirmation of renouncing your nationality to a diplomatic or consular officer in the US. You also lose citizenship if you officially renounce US nationality in another country.
• You were not eligible for naturalization or you intentionally provided incorrect data during naturalization test or in the N-400 Application for Naturalization form.
• You took part in a hostile actions against the US or you served in a foreign country army as an officer.
• You took an oath or any other type of formal statement of allegiance to a foreign country.
• You were employed by the other country’s government and your employment required you to declare allegiance to or to acquire nationality of the other country.

• You committed a treason against the US.

There are a couple of stipulations that apply to each of the mentioned cases. First, you may not lose the US citizenship if you were under eighteen when one of the listed infringements took place. For example, your parents may have decided to revoke your US citizenship when you were under eighteen. You only need to prove that you were underaged to become again a US citizen.

Second, you must exhibit intention when performing any of the actions we listed before. In case you were forced to, for example, serve for another country or government, you need to provide evidence that your action was not deliberate. In such a case, your US citizenship may be restored.

As we can see, there are few ways to lose US citizenship. You can always avoid expatriation or get US citizenship back if you have enough evidence to prove your real motives if any infringement happened in your case.