This article concerns the partially overlapping, but analytically discrete, options facing American leaders (and, indirectly, their allies) regarding the role of nu- clear weapons in strategy. Recent discussions of threat scenarios, in particular threats posed by environmental crisis or collapse, suggest that such fears are already shaping the grand strategy debate in the west - especially with respect to the issue of nuclear weapons retention. Accelerating environmental and economic crises will continue to narrow the grand strategy options avail- able to western governments. The Bush team's grand strategy of primacy is unlikely to outlast the administration. Grand strategy reform appears destined to result in either a defensively expansionist framework for cooperative im- perial liberalism or a possibly sudden retrenchment into siege mentality neo- isolationism following a major attack on the US or a close ally with weapons of mass destruction.1 Continued societal vulnerability coupled with increasing environmental and geostrategic instability suggests that strategic disengagement should be an American national security imperative, at least until an effective American system of perimeter defence screening and internal security detection of WMDs is developed.Selective engagement and off-shore balancing, while of perennial interest to advocates of classical realism, have too many defects and blowback liabilities. A grand strategy built mostly on selective engagement and off-shore balancing, with the risk of overseas interventions, might lead to ill feeling toward Americans and still feed the fires of nuclear or biological weapon terrorism or, worse still, the professional prepositioning of nuclear warheads.2 Were fears of WMD terrorism to spike because of some significant incident involving nuclear materials, neo-isolationism advocacy in the US might well become policy - but that is the only scenario currently conceivable for its ascendancy. Neo-isolationism simply lacks effective public or elite support. Ideological and foreign policy doctrinal orthodoxy suggests an evolved imperial order is more likely until such time as a catastrophic surprise occurs.3Cooperative security, while having enjoyed a brief period of advocacy in the first Clinton administration, remains the least promising option because of its exceptionally ambitious and costly approach to WMD proliferation. Justified American skepticism about the willingness of either leading allies or major powers to provide the required verification and enforcement capability for a robust arms control and disarmament system also undercut its appeal.4 Some cooperative security advocates would like to banish nuclear (and biological) arms to the extreme margins of international society through a detailed system of indirect deterrence based on disassembled virtual nuclear arsenals that would require lengthy times for reconstitution and use or, better still, permanently latent industrial production potential for nuclear and biological weapons.5 But despite recent public enthusiasm for rapid steps towards de-alerting and denuclearization, longstanding practical difficulties remain. The United Nation's impediments to security council reform, likely to be exacerbated by rising levels of environmental and geopolitical tension, are a further obstacle to any cooperative security regime for disarmament and collective security enforcement.Cooperative security will likely be written off as politically impractical and dangerous, and primacy will be jettisoned for having both alienated allies' opinions ofthe US and worsened the terrorist threat globally. As such, cooperative imperial liberalism - representing a possible hybrid version of primacy and cooperative security - may emerge as an interim winner in future US administrations trying to grapple with intractable nuclear and biological weapons proliferation amidst steadily worsening global environmental conditions. …