Israel's assassination of Hezbollah leader Hassan Nasrallah is a significant blow to the group and marks a turning point for Lebanon and the region. Nasrallah's death will shake the confidence of Hezbollah's allies and spark a shift in Iran's influence in the Middle East. Iran, Hezbollah's main backer, is in a policy dilemma on how to respond to retain its credibility. There is no clear successor to Nasrallah, and whoever replaces him will face a weakened force and growing anger at home. Rising tensions in Lebanon, coupled with the country's economic crisis, could lead to further instability.