"Labeiki ya Zaynab," chanted Iraqi Shiite fighters as they swayed, dancing with their rifles before TV cameras in Baghdad on June 13. They were getting ready for a difficult fight ahead. For them, it seemed that a suitable war chant would be answering the call of Zaynab, the daughter of Imam Ali, the great Muslim caliph who lived in Medina 14 centuries ago. That was the period through which the Shiite sect slowly emerged, based on a political dispute whose consequences are still felt until this day.

That chant alone is enough to demonstrate the ugly sectarian nature of the war in Iraq, which has reached an unprecedented high point in recent days. Fewer than 1,000 fighters from the Islamic State of Iraq and Syria (ISIS) advanced against Iraq's largest city of Mosul on June 10, sending two Iraqi army divisions (nearly 30,000 soldiers) to a chaotic retreat.

The call to arms was made by a statement issued by Iraq's most revered Shiite cleric, Grand Ayatollah Ali al-Sistani, and read on his behalf during a Friday prayers sermon in Kerbala. "People who are capable of carrying arms and fighting the terrorists in defense of their country ... should volunteer to join the security forces to achieve this sacred goal," the statement in part reads.