A dangerous power struggle between the Islamic Republic of Iran and the Kingdom of Saudi Arabia for dominance and control plagues the Middle East today. In a special three-hour series, FRONTLINE traces the modern history of this struggle from the 1979 Iranian revolution to the present day and investigates how the continued enmity of the two rivals is playing out in proxy wars from Iraq to Syria to Yemen and Lebanon. Filmed in seven countries over two years, the series examines how sectarian differences between Shia and Sunni Islam have been manipulated and deployed to sustain conflicts, all with devastating results. Bitter Rivals is a sweeping view of a region on fire with no end in sight.