Updated

A Columbia University professor who specializes in modern Korean and East Asian history has returned a 2014 prize he received from the American Historical Association after some sources in the winning book were questioned.

Charles K. Armstrong, author of "Tyranny of the Weak: North Korea and the World, 1950-1992," won the association's John K. Fairbank Prize, but came under criticism when more than 70 citations were challenged.

In response, Armstrong said he submitted 52 corrections for the book's next edition. On his website, he defended his work: "The errors did not cause serious damage to any scholarly field or to the validity of the book itself."

The American Historical Association , the largest professional organization serving historians, said last week that Armstrong returned the prize "out of respect" for the association.