RIYADH, Saudi Arabia — On Feb. 13, Ali Barakat uploaded a video to YouTube titled “Nasheed: Nasr bi-Yabrud,” or “Anthem: Victory in Yabrud.” Yabrud, a Syrian town about 80 kilometers (50 miles) north of Damascus, is the site of a battle between rebel groups and President Bashar al-Assad’s forces, who are supported by Shiite militant factions, including Hezbollah. The video shows footage of the conflict in Syria — advancing troops, firing tanks, a countryside in smoke — set to a pulsing pop song whose refrain promises, “I will decide your victory in Yabrud.” Barakat is a Lebanese singer and proud Hezbollah advocate. As of Feb. 18, the song has attracted more than 40,000 views and hundreds of comments pledging fealty to Hezbollah and wishing death upon its enemies.

This video — and thousands of other videos, photos, Facebook testimonials and websites like it — bear witness to a rapidly growing and little-understood phenomenon emerging in war-torn Syria. The Syrian revolution has ushered in the return of global Shiite jihad to the political arena, with an increasing number of Shiite militants arriving in Syria from around the world. Most of these fighters come from Iraq and Lebanon, with their numbers supplemented by recruits from Iran, Pakistan, Afghanistan, Yemen and some African countries. Scholars and journalists have not yet tackled the issue of Shiite militancy in depth. Most current research on the militants fighting in the Syrian revolution focuses on al-Qaeda and other non-Shiite organizations.

There are no reliable statistics available on the number of foreign Shiite fighters in Syria, but the latest estimates place their number between 10,000 and 15,000. Hezbollah fighters alone are estimated to be between 3,000 and 5,000, Iraqi fighters between 4,000 and 5,000 and Iranian Revolutionary Guard troops between 1,000 and 1,500. As of last month, between 300 and 400 Hezbollah fighters had been reported killed in Syria and around 2,000 injured. The battle of Yabrud is expected to increase these numbers significantly.

Observers of Iraqi Shiite militias in Syria have noticed the rise of an ideology linking current events in Syria to Shiite history and eschatology. The defense of the Shrine of Zeinab in Damascus, purported by Shiites to contain the tomb of first Shiite Imam Ali and his wife Fatimah’s daughter, has been invoked as a justification for war in the region. Many Shiite militias use slogans such as yali tharati al-hussein, or “revenge for Hussein,” and ya zaynab lan tusbay marratayn, or “O Zaynab, you will not be held captive twice,” evincing the belief that the current conflict is simultaneously a defense of Shiite sacred sites and an attempt at taking revenge on the Syrians for their role in the massacre at Karbala, which took place nearly 1,400 years ago. Nevertheless, this grafting of ancient grievances onto a contemporary conflict has its weak spots: Shiite militias may claim to act in defense of a single tomb in Damascus, but their wide-ranging and expanding military activities belie the sincerity of this goal.