The books garnered critical praise and attention for Sandburg, including the 1940 Pulitzer Prize for History for the four-volume "". But Sandburg's works on Lincoln also brought substantial criticism. William E. Barton, who had published a Lincoln biography in 1925, wrote that Sandburg's book "is not history, is not even biography" because of its lack of original research and uncritical use of evidence, but Barton nevertheless thought it was "real literature and a delightful and important contribution to the ever-lengthening shelf of really good books about Lincoln." Others criticized Sandburg's failure to document sources and factual errors. Others complain "The Prairie Years" and "The War Years" contain too much material that is neither biography nor history and is instead "sentimental poeticizing" by Sandburg. Sandburg may have viewed his book as an American epic more than as a mere biography, a view mirrored by other reviewers as well.