The Support for Diplomacy Scale (SDS) was developed to establish the unidimensional nature of peacemaking and militaristic attitudes. Across 5 studies, all 12 SDS items loaded strongly onto a single factor, with peaceful diplomacy at one pole and militarism at the other. The SDS was associated with authoritarianism (Studies 1–4) and dogmatism (Study 4), as well as measures of religious fundamentalism, immigration attitudes, universalism, and environmentalism (Study 2). In Study 3, the SDS mediated the relation between just peacemaking and measures of (a) voting intentions prior to the 2008 Presidential election, (b) militarism, and (c) resistance to moral disengagement from war. The SDS also predicted voting behavior in the 2008 Presidential election (Study 4) and mediated the relation between political orientation and foreign policy attitudes toward Iran (Study 5). Theoretical implications and statistical issues are discussed.