Sentence:  His political opponent and lifetime friend , Thomas Jefferson , achieved immortality through his authorship of the Declaration of Independence , but equally notable <WSD>were</WSD> the legal and constitutional reforms he instituted in his native Virginia , his role as father of our territorial system , and his acquisition of the Louisiana Territory during his first term as President . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)