Explore the modern-day origins of the intense political rivalry between Iran, which is largely Shia Muslim, and Saudi Arabia, which is mostly Sunni, for dominance over the Islamic world, in this video excerpted from FRONTLINE: Bitter Rivals. While a historical schism between Shias and Sunnis has existed since the 7th century, the violence that has come to characterize the power struggle in the region is a more recent product. It began nearly 40 years ago, with the Islamic Revolution led by Iran’s Ayatollah Khomeini. Khomeini’s doctrine was based on Islamic law and the rejection of Western domination. Because Iran perceives Saudi Arabia to be an ally of the United States, Iran is strongly opposed to the House of Saud.