Under what circumstances, if any, are preventive wars justifiable?
There is a broad consensus, in both international law and scholarship, that when a country faces a genuinely overwhelming and immediate threat, it may launch a proportionate attack to defend itself. That is a “pre-emptive” war. But what happens when a threat appears to be growing but isn’t truly dire or immediate? Should nations be permitted to launch “preventive” wars against their adversaries? The Iraq war has badly tarnished that idea — but two political scientists at the University of London are still willing to mount a lonely defense of the American invasion. In After Bush: The Case for Continuity in American Foreign Policy (Cambridge University Press, April), Timothy J. Lynch and Robert S. Singh argue that the rise of transnational terrorist movements has lowered the threshold for justifying a preventive war. “In the post-9/11 era,” they write, “it makes no sense to adhere without exception to norms that are eroding.” Even if a Democrat wins the presidency this year, Lynch and Si
