The agreement made last Saturday by the United States and Russia to eliminate Syria's arsenal of chemical weapons is not so unusual.
Two decades ago, during Yugoslavia's civil wars, diplomats in Moscow and Washington frequently concluded disarmament deals only to see these ignored even before the ink was dry on the documents. And the same may happen with this latest Syrian agreement.
Nevertheless, the deal is unique in both purpose and potential impact. Regardless of whether it succeeds or fails in its objective of disarming Syria, this document will define US President Barack Obama's foreign policy from now until the day he leaves the White House in early 2017. The stakes could not be any higher.
The temptation among commentators and diplomats is to assume that the US-Russia deal over Syria must have been hatched in secret talks over a longer period of time. After all, that's the story of most deals between these two former Cold War opponents. But the truth on this occasion is more boring: The deal is a haphazard arrangement intended to paper over botched policies in both Russia and the US and seized by both sides because both are actually weaker than either would care to admit.
President Obama's difficulties with persuading the US Congress to back a military intervention against Syria's chemical weapons dumps are well known, so Washington's eagerness to sign a deal which promises to achieve the same thing without firing a shot is understandable.
But Russian President Vladimir Putin is also in a similar bind. He knows that his vetoes in the United Nations Security Council will not prevent a US military operation against Syria.
He also knows that once such an operation has begun, Russia would be powerless to affect its outcome. In addition, the US military would have made mincemeat of the air defence systems which Syria bought from Russia, so the macho-strutting, judo-loving Mr Putin would have been served with a further humiliating reminder of just how technologically backward his country really is.
For all these reasons, the Russians also needed a deal which averted a military showdown.