Death of Osama bin Laden not the end of 'war on terror'
As the US enjoyed its moment of long-delayed catharsis, there was a tantalising sense that a decisive moment might have been reached.
"Killing Bin Laden is the end of the 'war on terror'," said Peter Bergen, a respected pundit on terrorism, on CNN.
The declaration of outright victory is likely to be as premature as it was in Afghanistan in 2001 and George W Bush's infamous claim of "mission accomplished" in Iraq in 2003. The US and its allies must brace for reprisals from al-Qaida cells and affiliates. The suicide blast at a Marrakech cafe and the arrest of three al-Qaida suspects in Germany last week were a reminder that the organisation's reach is still broad.
Instant suicide attacks may now be unleashed or plots still in the planning pipeline brought forward.
The level of violence could well spike as the disparate groups that carry the al-Qaida name aim to avenge the killing of their leader. If they fail to do so, their supporters and enemies alike could rightly question whether they are still a force to be reckoned with.
The struggle against international terrorism, and against al-Qaida in particular, does not give itself to neat beginnings and endings. The original idea of declaring a "war on terror" is now widely seen as a mistake. In 2009 the then foreign secretary, David Miliband, called for its abolition, saying it united the west's enemies rather than dividing them. Obama agreed and the phrase was quietly banned.
The danger posed by Islamist terrorists remains, but it is now more likely to be treated as a law enforcement and intelligence challenge rather than as an existential threat. Bin Laden's demise comes at a time when al-Qaida's influence is on the wane in the Arab and wider Islamic world. It has been conspicuous by its absence in the Arab Spring. To most of the revolutionaries in Tunisia, Egypt and Libya, Bin Laden was irrelevant. But it is still possible that disillusion, violence and the indecisive Nato intervention in Libya could create opportunities for jihadists.
The continuing challenge will require more coordinated international action. Bin Laden's greatest achievement after being driven out of Afghanistan in 2001 was to build an organisation that would survive him. The new al-Qaida is a loose global network, which in its most diluted form is little more than a franchise that groups around the world can sign up to, exchanging oaths of allegiance for the dread the name inspires.
In the absence of any plausible successor, that loose network is liable to fragment. Ayman al-Zawahiri, the aged, mumbling Egyptian doctor who has fulfilled the role of deputy since 1988, lacks Bin Laden's calm charisma.
With the decline of "al-Qaida central", subsidiaries will gain ground. Al-Qaida in the Arabian Peninsula could be an early forerunner. The Yemen-based group showed its ingenuity in November, smuggling bombs inside printer cartridges onto planes flying to the west.
However, al-Qaida today is less able to mount a spectacular mass-casualty outrage. The organisation has lost Bin Laden's grand ambitions and the cohesion necessary to launch a sophisticated attack.
Furthermore, as it now appears he was living in a compound in the heart of Pakistan and not in a remote cave, he may well have been playing more of a role in operational planning than many observers had thought.
But while the threat of a devastating attack on the west has receded, the constant menace of the suicide attack in a cafe, or the bomb on a plane, will be with us for some time to come.