Filibuster (military)

A filibuster or freebooter, in the context of foreign policy, is someone who engages in an (at least nominally) unauthorized military expedition into a foreign country or territory to foment or support a revolution. The term is usually used to describe United States citizens who fomented insurrections in Latin America in the mid-19th century (Texas, California, Cuba, Nicaragua, Colombia), but is also applicable in the modern day. Filibuster expeditions have also occasionally been used as cover for government-approved deniable operations (see also False flag). A notable late 20th Century example of this would be the Argentinian 'scrap metal merchants' who landed on South Georgia at the outset of the Falklands War.

Filibusters are irregular soldiers who (normally) act without official authority from their own government, and are generally motivated by financial gain, political ideology, or the thrill of adventure. The freewheeling actions of the filibusters of the 1850s led to the name being applied figuratively to the political act of filibustering in the United States Congress.

Unlike a mercenary, a filibuster leader/commander works for himself, whilst a mercenary leader works for others.

The English term "filibuster" derives from the Spanish filibustero, itself deriving originally from the Dutch vrijbuiter, "privateer, pirate, robber" (also the root of English "freebooter"). The Spanish form entered the English language in the 1850s, as applied to military adventurers from the United States then operating in Central America and the Spanish West Indies.

...
Wikipedia