Sentence:  And if the foreigners fighting in the Katanga Army <WSD>are</WSD> mercenaries then Lafayette and von Steuben were mercenaries too , as were also the members of the Lafayette Escadrille in the early part of World War 1 , and of Chennault 's Flying Tigers in the early days of World War 2 , . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)