Al-Qaeda’s success in carrying out the most devastating terrorist attacks ever meant that the dozen or so years since have seen American attention and resources dedicated to chasing down and dismembering the bin Laden network. That focus has implied a chronic failure to address other “terrorist groups of global reach,” to use Bush administration terminology.

In Hezbollah, Levitt of the Washington Institute for Near East Policy argues compellingly that none are more deserving of such attention than Lebanon’s Hezbollah or Party of God. In meticulous fashion, Levitt—a former FBI analyst and senior Treasury Department official—charts the organization’s political trajectory from its roots as an Iranian-sponsored, Syrian-supported offshoot of the Lebanese civil war to its current status as the Levant’s premier extremist actor. In the process, he demolishes a number of convenient, conventional myths about Hezbollah’s purported political moderation, its constructive role in Lebanese politics, and its ability to reconcile with Israel’s existence.

Levitt’s most significant contribution, however, lies in mapping the organization’s contemporary political footprint. In chapter after chapter, Hezbollah furnishes devastating details about how Iran’s chief terrorist proxy has emerged—and now thrives—far beyond its birthplace in Lebanon’s Bekaa Valley. Of particular note is Levitt’s review of Hezbollah’s longstanding presence in the Americas and the potential dangers that this holds for U.S. security.

Hezbollah stands as a definitive chronicle of the activities of Lebanon’s most notorious Shiite militia—and of the place that the group occupies in Iran’s strategic arsenal. Should Iran go nuclear, Hezbollah’s fortunes will turn yet further for the better—while those of Israel and the West would take a marked turn for the worse.