Turkey has been officially secular since 1924, although 99% of the population is Muslim. Most Turkish Muslims belong to the Sunni branch of Islam, but a significant number are Alevi Muslims. Questions of the goals of political Islam and the aftermath of the 1984-99 PKK Kurdish insurgency continue to fuel public debate on several aspects of Turkish society, including the role of religion, the necessity for human rights protections, and the expectation of security. Turkish citizens of Kurdish origin constitute an ethnic and linguistic group. Estimates of their population range up to 12 million.