And, third, this has all become harder. The reasons lie in US (and British) politics, as well as the wider international context. Following a series of less than totally successful wars, the British and American publics are in a mood of retrenchment. Disillusion has set in about the "New World Order" and the burden it has placed on those seeking to establish it. Both the British and American debates on Syria have been dominated by huge public aversion to any military intervention, even one as narrowly conceived as that originally planned by President Obama.

The international mood, too, is increasingly hostile to Western acts of military intervention. The trajectory of China and Russia, from endorsement of the Bosnia operation a decade ago to flat opposition in the case of Syria, is illustrative. These two countries have grown uncomfortable with the Western habit of overthrowing dictators well disposed to them (as in Iraq and Libya), and see the West's emphasis on human rights in global affairs as potentially a direct threat to their own regimes. But the problem goes wider. The discussion of Syria at the St Petersburg G20 summit last month showed that most major emerging countries (including India, Brazil, South Africa, Indonesia and Mexico) are not at all keen to see international norms adjusted to give the West greater scope to interfere in their internal affairs. These are the rising powers of the 21st century. They disliked US "unipolarity" under George W. Bush and see the authority of the UN Security Council, and strict adherence to the non-interference principle, as a key protection against it. While they did indeed, with gritted teeth, endorse the Responsibility to Protect, they did so in a form which in practice reaffirmed the blocking power of the Security Council. In the eight years since its adoption, Responsibility to Protect has not once been cited as a basis for UN action. 

So, is Bismarck back? Is the humanitarian moment over? There is one, by no means implausible, circumstance which would with absolute certainty bury the interventionist impulse: the emergence of some form of "Cold War" between the US and China. We would then once again be in a polarised world. All external political action would be judged by its effect on the balance between the great powers. Humanitarianism would again be an unaffordable distraction. 

But, absent a new superpower stand-off, Blair's 1999 arguments still ring true. The world is increasingly a village in which all our backyards adjoin. If your neighbour drives his children to hooliganism and petty theft, you will be among the victims. And the cries of his abused wife are distressingly audible in your kitchen. Massive repression in any country is no longer a domestic matter. A succession of crises — Kosovo, Libya, Syria — show that in today's closely linked world repression very quickly turns into an international tide of bad things: refugees, crime, terrorism. Protecting others from massive brutality is protecting ourselves at one remove. And nothing is now hidden. Thirty years ago, Bashar al-Assad's father Hafez killed 20,000 people to repress a revolt, and the world didn't really notice. His son's atrocities are on our TV screens every night. This is only one factor driving policy, but an important one.