King Banaian’s post at Liberty&Power (scroll down a bit) says that Mises’s view that interventionism prolonged the Great Depression does not appear to have been Rothbard’s. In fact, Rothbard’s America’s Great Depression only explained—and was only intended to explain as he explicitly points out in his Intro (p. xli)—the 1929-33 period. He does not treat the blizzard of crushing interventions that constituted Roosevelt’s New Deal, although he does discuss Hoover’s proto-New Deal policies that prolonged the recession through 1932. Rothbard also notes in his Intro (p. xlii) that he will contrast the public policies that explain the difference in duration between the brief 1920-21 depression and the 1929-33 depression. His explanation for the prolongation of the Great depression is no different than Mises’s.