In 1964, David McCullough began his writing career as an editor and writer for "American Heritage", which he sometimes calls "my graduate school". McCullough wrote numerous articles for the magazine. He turned his article for the June 1966 issue on the Johnstown Flood, "Run for Your Lives", into a full-length book titled, "The Johnstown Flood". When it became an unexpected bestseller, McCullough left the magazine in 1968 to commit full-time to writing. Later "American Heritage" articles by McCullough on the transcontinental railroad and Harry Truman also became bestselling books.