Smoke rises from the site of an Israeli airstrike in Beirut's southern suburbs on September 28.Joseph EidIsrael's assassination of Hezbollah leader Hassan Nasrallah was a major escalation.Nasrallah was one of Iran's most important allies.Iran's response could de-escalate the conflict or spark a wider war involving major global powers.Israel's assassination of Hassan Nasrallah, the head of Hezbollah for over 30 years, is a major escalation in the Middle East conflict.De-escalation is now up to Iran.Nasrallah was Iran's most trusted proxy in its conflict with Israel and its power struggle with Saudi Arabia and the United States.