War and terrorism, which are inseparable, cause death and disability, profound psychological damage, environmental destruction, disruption of the health infrastructure, refugee crises, and increased interpersonal, self-directed and collective violence. Weapons systems such as weapons of mass destruction and landmines have their own specific devastating effects. Preparation for war and preparedness for terrorism bring constraints on civil liberties and human rights, increase militarism, and divert resources from health care and from other needed services. War and terrorism may be best prevented through addressing their causes, which include limited resources, injustice, poverty and ethnic and religious enmity, and through strengthening the United Nations and the treaties controlling specific weapons systems, particularly weapons of mass destruction. In particular, the United States should cease its interference in the internal affairs of other nations and its advocacy of unilateral pre-emptive war.