To study how attitudes and social psychological processes influence decisions about war and peace, a 15-question scale was developed to measure moral disengagement in support for military action. In a survey of 128 secondary school students in the USA and Finland, the scale demonstrated acceptable reliability (0.85-0.90) in different gender and national groups. US students were less morally engaged than Finnish students and males were less morally engaged than females. Scale scores were strongly related to the students' support for US and NATO military actions in Iraq and Yugoslavia. In a second study, 73 US university students participated in a brief, randomized experiment comparing the effects of contrasting communications on moral disengagement in support for military action. After completing a pretest survey, the students were randomly assigned to persuasive communications favoring either moral disengagement or resistance to moral disengagement. Immediately after they received these communications, the students were given the opportunity to give new answers to the survey questions about moral disengagement and approval of specific military actions. Analyses of pretest data confirmed the reliability of the scale and its ability to predict opinions about the US and NATO bombing campaigns in Iraq and Yugoslavia. Analyses of change scores showed increasing moral disengagement in one group and decreasing moral disengagement in the other group, in accordance with the type of communication that was provided between surveys. The groups also differed significantly in their changes of opinions about the NATO bombing of Yugoslavia and in their subsequent willingness to sign letters of praise or protest for their US Representative's congressional vote against the bombing.