But while history can tell us a great deal about the evil ideology can wreak, sadly, the power of ideology is very far from being history. The ideology of Islamism - the force which unites Osama bin Laden, Hizbollah, the killers in Mumbai and the murderers of Madrid, the architects of 9/11 and the authors of 7/7 - drives men to slaughter in the name of a sacred cause. These killers do not care if innocents are killed, but while they revel in indiscriminate slaughter they do discriminate, where they can, by choosing Jewish targets whenever possible. Not Israeli, not Zionist. Jewish.

The choice of New York on 9/11, the targeting of a Jewish community centre in Mumbai, the pledge by Hizbollah to target Jews wherever they lived, all show that the murderous prejudice that drove the Arrow Cross to do evil in the ruins of Budapest 60 years ago survives in all its rampant ugliness today. And, therefore, when we look at the conflict in Gaza, we must never be blind to the ideology at work there. Our eyes will, inevitably, be clouded by tears. Each man's death diminishes us and no one can be indifferent to the suffering of innocents, especially so many children, caught up in the fighting. Every moral sense we have impels us to want the fighting to cease.

But moral sense also prompts us to ask what lies behind this conflict. And the implacable persistence of ideology is the key. This is not primarily a conflict about territory. There is a struggle over territory between Israel and the Palestinians that must be resolved. There are hard questions about borders, barriers and Jerusalem that we need to address if we are to reach a settlement with a secure Israel and a viable, democratic, Palestinian state in the future.