Sentence:  “For 300 years as bondsmen and some 93 years as freemen, under slaver's whip and Jim Crow law,” Mr. Jackson wrote in The Daily Worker in 1958, “Negro Americans have yielded up their labor and expended their lives for the <WSD>upbuilding</WSD> of this country in yet unfathomed measure.” 
Meaning of the word marked with <WSD> tags:  To build up; to develop (figuratively).