The term filibuster was predominantly used to describe United States citizens who engaged in unauthorised military expeditions into foreign countries, either to foment insurrections or usurp that country’s government.
The high watermark of filibuster activity was around the mid 19th century when a number of expeditions were launched aiming to take control of various Caribbean, Mexican, and Central-American territories, including John Quitman in Cuba, William Walker in Baja California, Sonora, and Nicaragua, and Henry Alexander Crabb in Sonora.
Although strictly prohibited by the Neutrality Act of 1794, the filibusters were rarely prosecuted by the American government. On the rare occasions when U.S. authorities did press charges, the filibusters were usually acquitted by American juries intoxicated by the idea of Manifest Destiny.
The age of filibustering eventually came to an end as Manifest Destiny fell out of favour with the coming of the American Civil War.