Today, too, skillful politicians have proved adept at using democratic structures to erect forms of authoritarian rule. President Vladimir Putin has gradually moved Russia, a country increasingly flexing its muscles internationally again, in that direction. Venezuela, under President Hugo Chávez, has also showed distinct authoritarian tendencies, though these have been at least partly blocked through his defeat in the December referendum to change its constitution.

In Zimbabwe, President Robert Mugabe has turned democracy into personal rule, ruining his country in the process. In Pakistan, democracy largely provides a facade for military rule, even if President Pervez Musharraf has now put aside his uniform. Most worryingly, perhaps, President Mahmoud Ahmadinejad of Iran has used populist support in a pluralist system to push Iran into a hazardous foreign policy, though he does remain formally subordinate to the "supreme leader," Ayatollah Ali Khamenei.

None of these examples, however, poses a close parallel to what happened in Germany in 1933. Neo-fascist movements in Europe can certainly terrorize minorities. And they have had success in stirring such resentment about immigrants that mainstream political parties have taken account of the swell of feeling.

However, short of some unforeseeable eventualities like major war or, perhaps less unlikely, another meltdown of the economic system, neo-fascist movements will remain on the fringes of politics. And none of these parties can today conceive of preparing for a war of conquest.

Elsewhere, there are - and always will be - nasty forms of authoritarianism. But neither in their acquisition of power nor in their use of it do modern authoritarian rulers much resemble Hitler. International organizations and institutions that did not exist in interwar Europe - the United Nations, the European Union, the World Bank, the International Monetary Fund - also provide barriers to the sort of calamity that engulfed Germany.

Moreover, democracies under pressure can still pose obstacles to creeping authoritarianism. Putin looks as if he will indeed step down as president and not risk a breach of the constitution (though effective power will probably remain in his own hands), while Chávez has been forced (maybe temporarily) to give up his ambitions to become a president for life.

Mercifully, what happened in Germany in 1933, and its aftermath, will remain a uniquely terrible episode in history. What took place then reminds us even so of the illusory assumption that democracy will always be a favored choice of a population torn apart by war, facing enormous privations and burning with resentment at national humiliation through perceived foreign interference. It also reminds us of the need for international cooperation to restrain potential "mad dogs" in world politics before they are dangerous enough to bite.

Ian Kershaw, a professor of modern history at Sheffield University, is the author of the forthcoming "Hitler, the Germans and the Final Solution."