ABSTRACT
The twentieth century opened with many predictions that the age of war was over, especially in Europe. There were many reasons for this optimism. Arbitration of international disputes had become increasingly common. The American Civil War and the Crimean War had demonstrated the horror of war with modern weaponry: This would surely cause leaders to hesitate before starting another war. There was also philosophical justification for optimism. Enlightenment thinkers had often addressed the pursuit of peace. Voltaire had thought that religious toleration was the key to peace. Rousseau had instead argued that the popular will was generally opposed to war: The replacement of kings with assemblies was necessary to achieve peace. Many international organizations emerged in the late nineteenth century that advocated for peace. These often had links to women’s groups or worker organizations. Some had religious support. Their efforts to encourage states to pursue peace had limited success.
