Almost two thirds of the population of Iraq 60-65% are Shia Muslims.
In addition, Iraq is the site of the holy cities of Najaf and Karbala, pilgrimage sites for millions of Shi'a Muslims. Najaf is the site of the tomb of Ali ibn Abi Talib (the first Shi'a Imam), and Karbala is the site of the tomb of the grandson of Muhammad and Shī‘ah Imām, Husayn ibn Ali. Najaf is also a center of Shi'a learning and seminaries. Two other holy sites for Twelver Shia in Iraq are the Al-Kadhimiya Mosque in Baghdad, which contains the tombs of the seventh and ninth Shī‘ah Imāms, Mūsā al-Kādhim and Muhammad at-Taqī, and the Al-Askari Mosque in Sāmarrā, Iraq which contains the tombs of the tenth and eleventh Shia Imams, Ali al-Hadi and Hasan al-‘Askarī.
Southern Iraq has been Shia since the 4th caliph of Sunni Islam and the 1st Imam of Shia Islam moved the capital of the empire from Medina to Kufa/Najaf only two decades after the death of the Prophet Muhammad. Thus Imam Ali and 6 other of the total 12 Imams of the Shias are buried in the Shia areas of Iraq. In fact, Iraq is the birth place and the first Shia country in the world, long before Iran, Lebanon or Azerbaijan. It was the message and the preacher from Iraq that in time converted Iran and taught them the principle of Shiism when the Shia Safavid dynasty declared Shiism the official religion of Persia in AD 1501.