Neorealists conclude that because war is an effect of the anarchic structure of the international system, it is likely to continue in the future. Indeed, neorealists often argue that the ordering principle of the international system has not fundamentally changed from the time of Thucydides to the advent of nuclear warfare. The view that long-lasting peace is not likely to be achieved is described by other theorists as a largely pessimistic view of international relations. One of the main challenges to neorealist theory is the democratic peace theory and supporting research, such as the book "Never at War". Neorealists answer this challenge by arguing that democratic peace theorists tend to pick and choose the definition of democracy to achieve the desired empirical result. For example, the Germany of Kaiser Wilhelm II, the Dominican Republic of Juan Bosch, and the Chile of Salvador Allende are not considered to be "democracies of the right kind" or the conflicts do not qualify as wars according to these theorists. Furthermore, they claim several wars between democratic states have been averted only by causes other than ones covered by democratic peace theory.