Original sentence: After rising through the academic ranks --- lecturer and reader --- by 1997 he became the University's second professor of American history, or its first exclusive professor of American history, given that in 1965 George "Sam" Shepperson had became "Professor of Commonwealth and American History.Building on his work involving private detectives who collected intelligence for big business, Jeffreys-Jones then shifted his scholarly focus during the late 1970s to examine American secret intelligence, a time when the field began to blossum with the release of historical records and revelations of American intelligence agencies' activities
Edited sentence: After rising through the academic ranks --- lecturer and reader --- by 1997 he became the University's second professor of American history, or its first exclusive professor of American history, given that in 1965 George "Sam" Shepperson had become "Professor of Commonwealth and American History.Building on his work involving private detectives who collected intelligence for big business, Jeffreys-Jones then shifted his scholarly focus during the late 1970s to examine American secret intelligence, a time when the field began to blossom with the release of historical records and revelations of American intelligence agencies' activities