What religion was Turkey before Islam?

Pre-Islamic Religion in Turkey

Before the arrival of Islam, the majority of Turkic peoples practiced Tengrism, which involved the worship of the sky god Tengri. In addition to this, there were also some followers of Manichaeism, Nestorian Christianity, and Buddhism. However, during the period of Muslim conquests, the Turks entered the Islamic realm primarily as captives, as a result of Arab raids and military campaigns.