If you meander through the history of the 1930s, you will find any number of possible parallels with today's crisis in Eastern Europe. Aggressive powers, namely Germany and Italy, challenged the existing order by attacking or annexing weaker nations. Today some American politicians are warning that "appeasing" Vladimir Putin -- which is meant to invoke the infamous Munich Conference of 1938 -- will only lead to more war. But such parallels are weak, says historian Ian Kershaw, the author of an unparalleled, two-volume biography of Hitler. If there is anything to learn from the 1930s, it is the importance of not drawing the wrong lessons. Still, some comparisons may work. That is, the inherent weaknesses of democracies, then and now, in facing up to the threats of dictators. And Kershaw stresses the importance of ideological motivations on the part of such figures as Hitler and Putin -- motivations that were overlooked by the West.