The expratiation is the loss of nationality. Usually is voluntary and it is applied to those who have renounced nationality and citizenship in one country to became citizens of another. Examples of voluntary expatriation happen when a citizen becomes naturalized in a foreign state. A more general type of expatriation is the loss of nationallity that occurs with the cession or conquest of a territory. This is a doctrine set by the United States in 1868 that challenged the thinking of those times, untill that time someones allegiance couldn´t be rennounced without the state´s permission. But the United States did it in order to protect its naturalized inmigrants against the claims of their native states. The Congress declares that voluntary expatriation was a natural and inherent right to all people.
But lets focus on involuntary expatriation, this happen when is the government who decides to renounce it´s obligation to individuals. I will give a historic example, prior to 1922 an American woman who married an alien was automatically expatriated but after that year a resolution nulified that and let women to maintain their citizenship unless they make a formal renunciation. Nowadays the expatriation can be set in motion by deserting during wartime, it is common among some countries including United States that the voluntary expatriation during time of war gets forbidden. The involuntary expatriated individuals are stateless untill naturalization under some other government. Finally in the U.S. territory there is a law called the Enemy Expatriation Act and it allow the government to strip U.S. citizenship to those person who participates in terrorist activities, defined as providing material, support or resources to Foreign Terrorist Organization or actively engaging in hostilites against the United States or its allies.
I hope this answer help you and that it is correct. Regards.