Islam is the largest religion in Indonesia, with 86.7% of the Indonesian population identifying themselves as Muslim in a 2018 survey. Indonesia is the most populous Muslim-majority country, with approximately 231 million adherents. In terms of denomination, the overwhelming majority (98.8%) are Sunni Muslims, while 1-3 million (1%) are Shia, and are concentrated around Jakarta, and about 400,000 (0.2%) Ahmadi Muslims. In terms of schools of jurisprudence, based on demographic statistics, 99% of Indonesian Muslims mainly follow the Shafi'i school, although when asked, 56% does not adhere to any specific school. Trends of thought within Islam in Indonesia can be broadly categorized into two orientations: "modernism", which closely adheres to orthodox theology while embracing modern learning, and "traditionalism", which tends to follow the interpretations of local religious leaders and religious teachers at Islamic boarding schools (pesantren). There is also a historically important presence of a syncretic form of Islam known as kebatinan. Islam in Indonesia is considered to have gradually spread through merchant activities by Arab Muslim traders, adoption by local rulers, and the influence of Sufism since the 13th century. During the late colonial era, it was adopted as a rallying banner against colonialism. Today, although Indonesia has an overwhelming Muslim majority, it is not an Islamic state, but constitutionally a secular state whose government officially recognizes six formal religions. Distribution Muslims constitute a majority in most regions of Java, Sumatra, West Nusa Tenggara, Sulawesi, coastal areas of Kalimantan, and North Maluku. Muslims form distinct minorities in Papua, Bali, East Nusa Tenggara, parts of North Sumatra, most inland areas of Kalimantan, and North Sulawesi. Together, these non-Muslim areas originally constituted more than one-third of Indonesia prior to the massive transmigration effort sponsored by the Suharto government and recent spontaneous internal migration. Internal migration has altered the demographic makeup of the country over the past three decades. It has increased the percentage of Muslims in formerly predominantly-Christian eastern parts of the country. By the early 1990s, Christians became a minority for the first time in some areas of the Maluku Islands. While government-sponsored transmigration from the heavily-populated Java and Madura to less-populated areas contributed to the increase in the Muslim population in the resettlement areas, no evidence suggests that the government intended to create a Muslim majority in Christian areas, and most Muslim migration seemed spontaneous. Regardless of its intent, the economic and political consequences of the transmigration policy contributed