Even the demonstrative use of a lower-yield tactical nuclear weapon by Russia would mark the end of the postwar order through which, under U.S. leadership, most of the world enjoyed relative and increasing levels of prosperity, freedom, and peace. It would augur the beginning of an era more like that of 1914-45, scarred by the Great Depression, totalitarianism, genocide, and world wars that included the use of chemical and nuclear weapons of mass destruction and killed as many as 100 million people.