One consequence of the Iraq war is to expose (once again) the false divide between "civilized" and "barbarous" nations. The United States seems as capable of barbarism as anyone else, as the abuses at the Abu Ghraib prison make clear. Much of the time the barbarism in Iraq goes unrecorded, as when American tanks sweep into Iraqi neighborhoods and kill dozens of innocents in the name of fighting "insurgents." But barbarism is found in many quarters, as the grisly beheading of an American hostage made clear.
Every society, under certain conditions, is vulnerable to a descent into barbarism. Many historians have argued that German society under Hitler was somehow uniquely evil. False. Germany was destabilized by defeat in World War I, a harsh peace in 1919, hyperinflation in the 1920's, and the Great Depression of the 1930's, but was otherwise not uniquely barbarous. On the contrary, in the early part of the twentieth century, Germany was one of the world's richest countries, with enviably high education levels and scientific prowess. Hannah Arendt was closer to the mark when she wrote about the "banality of evil," not its uniqueness.
There seem to be two common characteristics of the descent into barbarism. The first is the relentless human tendency to classify the world as "us" versus "them," and then to reduce "them" to sub-human status. Such classifications probably evolved because they strengthened the cohesion of the "in" group, facilitating cooperation by harnessing hatred for those outside.
Hatred and violence against "others" seem to be manifested most powerfully as the result of fear: they are survival reactions. The descent into barbarism generally occurs in the midst of economic crisis or when localized violence has already flared. Fear leads one group to coalesce in order to protect itself, perhaps by attacking a competing group.