What term is used to describe an adventure seeker who causes rebellion in a foreign country?

The term "filibuster" specifically refers to an adventurous individual who engages in unauthorized military or paramilitary actions in a foreign country, often to incite rebellion or promote a particular political agenda. This term has historical roots in the context of American expansionism during the 19th century, where various individuals sought to overthrow governments or seize territories – typically for personal gain or to advance a specific cause.

In contrast to other terms, a revolutionary generally refers to someone involved in a significant movement seeking to outright change the government within their own country, while a patriot denotes a person who loves their country and may work to enhance it, usually within its established framework. An insurgent is someone who rises in revolt against an established authority, but this term often describes a group rather than the individualistic and adventurous connotation associated with filibusters. Thus, the unique characteristics of a filibuster best match the description provided in the question about an adventurer causing rebellion in another country.