For the United States the ‘international law of global security’ is, in a unique sense, synonymous with the entire project of constructing global legal order. Uniquely preponderant power enjoyed since the end of the Second World War has allowed US preferences to manifest not merely in specific rules and regimes, but in purposive development of the entire structure of global legal order to favour American security interests. Perceptions of a recent decline in this order now find expression in advocacy for a ‘liberal’ or ‘rules-based’ international order, as the claimed foundation for global prosperity and security. This working paper seeks to map out the parameters of US contributions to the global security order by uncovering the strategic and political foundations of its engagement with the international law of global security. The paper begins by reflecting on competing US conceptions of the relationship between national security and global order as they evolved across the twentieth century. The focus then turns to three significant trends defining the contemporary field. First are US attitudes toward multilateral institutions and global security, and the ongoing contest between beliefs that they are mutually reinforcing versus beliefs that US security and global institutions sit in zero-sum opposition. Second is the impact of the generational ‘War on Terror’, which has yielded more permissive interpretation and development of laws governing the global use of violence. The final trend is that towards competitive geopolitical interests restructuring international law, which are evident across diverse areas ranging from global economics, to cybersecurity, to the fragmentation of global order into spheres of influence. Looking ahead, a confluence of rising geopolitical competitors with divergent legal conceptions, and conflicted domestic support for the legitimacy and desirability of US global leadership, emerge as leading forces already reshaping the global security order.