In a 1999 book published by the Ludwig von Mises Institute, Hoppe asserted that Rothbard was the leader of the "mainstream within Austrian Economics" and contrasted Rothbard with Nobel Laureate Friedrich Hayek, whom he identified as a British empiricist and an opponent of the thought of Mises and Rothbard. Hoppe acknowledged that Hayek was the most prominent Austrian economist within academia, but stated that Hayek was an opponent of the Austrian tradition which led from Carl Menger and Böhm-Bawerk through Mises to Rothbard. Austrian economist Walter Block says that the Austrian School can be distinguished from other schools of economic thought through two categories—economic theory and political theory. According to Block, while Hayek can be considered an Austrian economist, his views on political theory clash with the libertarian political theory which Block sees as an integral part of the Austrian School.