Sentence:  <WSD>Filibusters</WSD> were American citizens who used armed force to procure economic and political influence beyond the borders of the United States from 1848–1861. Their efforts were directed mainly southward toward Cuba, Mexico, and the Central American republics. These illegal excursions disrupted diplomatic relations of the United States within its own hemisphere by damaging relations with Latin American countries and the United Kingdom. 
Meaning of the word marked with <WSD> tags:  A mercenary soldier; a freebooter; "specifically", a mercenary who travelled illegally in an organized group from the United States to a country in Central America or the (Spanish West Indies) in the mid-19th century seeking economic and political benefits through armed force.