A filibustering expedition is an irregular, unauthorized attack which proceeds from the territory of one state against that of a friendly state. Once such an expedition merges with the armed forces opposed to the legal government of a friendly state, it ceases to be a filibustering movement. If however its organization remains intact and merely attracts recruits from among the rebels, it retains its filibustering character. Because of their clandestine nature, secrecy and deception characterize the formation of filibustering expeditions. Plots and intrigues are formed, disrupted, and formed again.....The main actors, as John Quincy Adams remarked, cross and double-cross one another so frequently that suspicion and doubt hang like a black cloud over all of their actions---Warren in The Sword Was Their Passport.
As independent thought and movements mounted in the period 1800 through 1821 aimed at the separation of Mexico from Spain, Texas and northern Mexico became a fertile target for filibusters from a number of countries and most commonly the bordering United States, a Spanish ally. The separation between trade expeditions and adventurous wandering, both authorized and unauthorized, and filibuster expeditions, and motivations of each, personal profit versus political, is a thin line and continuously debated among historians.