Except perhaps for such irreducible sexual groups as parents and their children, the ‘man’ of classical liberalism (whose literary symbol was Robinso… - Eric Hobsbawm

[H]istorians are to nationalism what poppy-growers in Pakistan are to the heroin-addicts: we supply the essential raw material for the market. Nations without a past are contradictions in terms. What makes a nation is the past, what justifies one nation against others is the past, and historians are the people who produce it. So my profession, which has always been mixed up in politics, becomes an essential component of nationalism.

Under these circumstances of social and political disintegration, we should expect a decline in civility in any case, and a growth in barbarism. And yet what has made things worse, what will undoubtedly make them worse in future, is that steady dismantling of the defences which the civilization of the Enlightenment had erected against barbarism, and which I have tried to sketch in this lecture. For the worst of it is that we have got used to the inhuman. We have learned to tolerate the intolerable.
Total war and cold war have brainwashed us into accepting barbarity. Even worse: they have made barbarity seem unimportant, compared to more important matters like making money.

In the simplest terms the question who or what caused the Second World War can be answered in two words: Adolf Hitler.