Another major division within Islamism is between what Graham E. Fuller has described as the fundamentalist "guardians of the tradition" (Salafis, such as those in the Wahhabi movement) and the "vanguard of change and Islamic reform" centered around the Muslim Brotherhood. Olivier Roy argues that "Sunni pan-Islamism underwent a remarkable shift in the second half of the 20th century" when the Muslim Brotherhood movement and its focus on Islamisation of pan-Arabism was eclipsed by the Salafi movement with its emphasis on "sharia rather than the building of Islamic institutions," and rejection of Shia Islam. Following the Arab Spring, Roy has described Islamism as "increasingly interdependent" with democracy in much of the Arab Muslim world, such that "neither can now survive without the other." While Islamist political culture itself may not be democratic, Islamists need democratic elections to maintain their legitimacy. At the same time, their popularity is such that no government can call itself democratic that excludes mainstream Islamist groups.