A common factor among the classical theories was the agreement that the history of humanity is pursuing a fixed path. They differed on where that path would lead: social progress, technological progress, decline or even fall. Social cycle theorists were skeptical of the Western achievements and technological progress, but argued that progress is an illusion of the ups and downs of the historical cycles. The classical approach has been criticized by many modern sociologists and theorists; among them Karl Popper, Robert Nisbet, Charles Tilly and Immanuel Wallerstein.