At last they've got him. There's not much good news from Europe at the moment, but the fact that Ratko Mladic is sitting in the detention cell of an international tribunal in The Hague is a cause for unqualified celebration. The man directly responsible for the massacre of about 8,000 unarmed men and boys at Srebrenica will now be held to account for that and other atrocities. This is another step forward in one of the great developments of our time: the global movement toward accountability.
Just over 60 years ago, Polish poet Czeslaw Milosz wrote a poem addressed to the torturers and mass murderers of one of the bloodiest periods in European history. "You who harmed an ordinary man," he warned, "do not feel safe." People may heap sycophantic praise on you now, but "the poet remembers."
Back then, that was about all your mass murderer had to be frightened of: the poet remembering.
A post-1945 moment of very imperfect international accountability, symbolized by the Nuremberg trials of Nazi leaders and the founding treaties of international humanitarian law, faded behind the instrumental amnesias of the Cold War. Monsters died in their beds, their medals still hanging from the uniform in the wardrobe. Only the poet remembered; the poet, and the ordinary person, if still alive.
But those post-1945 ideals never quite died. From the 1970s onward, many different forms of accountability were developed worldwide: truth commissions, judicial investigations, the opening of archives, banning compromised people from holding public office, domestic and international trials.
All have their proper place, but an international court is the best way yet discovered to deal with the vilest of the vile: those credibly accused of crimes against humanity. In national courts, there are generally legal contortions and the strong suspicion of a partisan political agenda.
International courts, such as the special tribunal for the former Yugoslavia, which holds Mr. Mladic, and the International Criminal Court, are also open to multiple objections. Apart from the slowness of the judicial process, which resulted in former Serbian leader Slobodan Milosevic dying unconvicted in The Hague, most of these objections come down to the charge of double standards.
Why, cry many Serbs, do you arraign only Serbs, not Croats and Bosnians?
That accusation is simply false. Beside Messrs. Milosevic, Mladic and Radovan Karadzic, the tribunal has convicted Croat general Ante Gotovina and is currently retrying Ramush Haradinaj, a Kosovar Albanian guerrilla leader.
Why, say others, do you fry the big fish and let the little ones swim free?
That is true, but inevitable. You cannot try all the tens of thousands responsible, in different degrees, for the horrors of any dictatorship. If you can only do a few fish, I say fry the big ones.
Then there's the objection, "Why do you prosecute X but not Y?" Why Mr. Milosevic and Liberia's Charles Taylor, but not Than Shwe of Burma or Bashar al-Assad of Syria? To this there are several answers.
One is: If you can't catch all murderers, that doesn't mean you shouldn't catch any. Another is maybe the ICC should be prosecuting Y too. And a third: Differential responses don't always mean double standards.
If a leader oversteps the very extreme mark that qualifies one for a charge of crimes against humanity, then he or she should be liable to prosecution in an international court. If, however, their past misdeeds fall short of that very demanding standard, there is room for local understandings.
If the leader has consented to a peaceful negotiation from dictatorship, that good conduct should be taken into consideration. For example, it is quite wrong that the Polish martial law leader Wojciech Jaruzelski, who was not guilty of crimes against humanity and tried to make amends by helping Poland's transition to democracy in 1989, should still - as a very old man - be on trial for those earlier misdeeds.
The most difficult choice would come if a leader such as Moammar Gadhafi in Libya, who has terrorized his people and certainly merits prosecution, were then to play a Jaruzelski-type part in a negotiated transition. But there is no sign of that.
In the rest of the world, the charge of double standards is mainly directed against the West, especially the United States. From Latin American dictators to the current rulers of Saudi Arabia - so runs a popular argument - Washington's tyrannical friends have got away with murder while its foes are liable to be assassinated. Over the past 60 years, there have been too many individual instances of such extreme double-standards. However, I emphatically don't think the killing of Osama bin Laden belongs on that list. Yes, in some ideal world, Mr. bin Laden would now be sitting in a cell in The Hague. But does anyone seriously believe that the Pakistani security services could have been relied on to deliver him to an international court?
In general, if international law is to have any chance of deterring the monsters of tomorrow, then we need the United States to support it practically and not just rhetorically. That means applying international law to itself, not just to others. At the moment, the U.S. is not even a member of the ICC.
There is nothing irreversible about the movement toward accountability. If the profoundly satisfying thing that happened this week to Mr. Mladic is to have any chance of becoming an international norm, rather than a transient European exception, then the United States must throw its weight behind the kinds of institution that will make this possible. To celebrate this arrest, the U.S. should join the International Criminal Court.
Timothy Garton Ash is professor of European studies at Oxford University and senior fellow at the Hoover Institution.
Follow us on Twitter: