The way in which the Government's defeat in the House of Commons last week was reported, one would think that Britain had vowed never to send troops further than Dover again.
Cameron's rather petulant reaction to losing the vote: "I get that and the government will act accordingly" suggested that he was so confident of winning and had no plan B. That may be why people are calling it the end of an era. It isn't. What is clear from the vote is that the 'NOs' were a very mixed group, motivated from passivism to isolationism combined with a powerful Deja Vu of Iraq 2003.
Then Parliament was persuaded to attack Iraq by Tony Blair using what turned out to be false intelligence. Now it is clearly wary of following the Americans wherever they want to go. Until those who provided and accepted that false information in 2003 are held to account, it will be difficult to expunge that horrific miscalculation. Why aren't George Bush, Tony Blair and others being pursued by the International Criminal Court?
It is also clear that many parliamentarians wanted to wait until the UN inspectors had reported. So why did Cameron not hold a debate on the issue, get a sense of the House but delay a vote until the inspectors had reported?
And why did the Americans not release their intelligence earlier? It is a fascinating bag of intercepts and other data which proves the Assad regime was the perpetrator and is probably, if the sources are trusted, more conclusive than the inspectors' report will ever be.
But just as it looks as if Britain is going to be isolated, Obama has followed suit and decided to allow Congress a vote on intervention in Syria next week. Will he win it? Will France - for a brief and improbable moment, a closer ally of the United States than Britain - also be forced to hold a vote? What is clear is that the mood is very febrile. The same debate in any of these countries could be held in two successive weeks and produce opposite results.
In the case of Syria, the issue is whether or not to punish the Assad regime, destroy the chemical weapon making facilities and, hopefully, tip the balance of power in the 'right' rebels' favour. Amongst the opposition to Assad are bound to be some Al Qaeda fighters. That would deter putting Western troops on the ground if the civil war in Syria gets worse. So you drop a few bombs, perhaps wreck the military headquarters and the chemical weapons factory - hopefully not releasing even more poison gas in the process - and help the 'good guys' win.
The experience of intervention in the Arab Muslim world so far, however, seems to be that while superior firepower can help overthrow brutal dictators, foreign armies have then got ambushed by fundamentalist Islamic fighters and suicide bombers that have emerged from the wreckage. These opponents can be contained, but probably not defeated, by weapons.
The greatest irony of this era in the Middle East is that the two rulers most committed to crushing Islamic fundamentalism in the Arab world, Saddam Hussein and Colonel Gadaffi, were overthrown by the West. And in Afghanistan and Iraq, Western countries won the war but failed to replace the dictators with effective governments.
It is vital that the fundamental principal of the responsibility to protect is not washed away in Parliament's rejection of an attack on the Syrian government. One of the best global developments at the end of the 20th Century was the establishment of the duty to help civilians everywhere in the world caught up in civil wars or deliberately attacked by the armed forces of states or rebel militias.
Freed from Cold War logic of global political bifurcation, the liberal democracies were free to intervene wherever international law had been broken or civilians were under threat. The expulsion of Iraq from Kuwait by a coalition of 32 countries was the first, hugely successful, intervention.
The second intervention in Somalia in 1992 was successful at first, but the UN was unable to restore the Somali state. That intervention ended in the 1993 Blackhawk down disaster and when America walked away, Somalia was left to stew for another two decades of civil war.
The following year, the Rwandan government carried out genocide but America and Britain ignored it. The Defence Department in Washington slowed up the delivery of military vehicles to the small UN force that was on the ground and blocked further intervention at the UN. By the time any UN reinforcements did arrive in Rwanda, the genocidaires had been defeated by the Rwanda Patriotic Front, led by Paul Kagame.
This failure - acknowledged by Clinton, Kofi Annan and others - gave huge momentum to the call for the Responsibility to Protect which was finally agreed by the UN in 2006. Its principles are:
A state has a responsibility to protect its population from genocide, war crimes, crimes against humanity, and ethnic cleansing.
The international community has a responsibility to assist the state to fulfill its primary responsibility.
If the state manifestly fails to protect its citizens from the four above mass atrocities and peaceful measures have failed, the international community has the responsibility to intervene through coercive measures such as economic sanctions. Military intervention is considered the last resort.
Apart from the restoration of the state of Kuwait in 1991, the successes of western intervention have all been outside the Muslim world. In former Yugoslavia, the West moved to protect Bosnian Muslims.
In Sierra Leone, Sir David Richards, the army commander, and Peter Penfold, the British High Commissioner, persuaded a sceptical Blair to allow the British evacuation force which had come to rescue British soldiers captured by rebels, to stay on and defeat the rebels. The French intervened briefly in Cote d'Ivoire in 2011 to stop Laurent Gbagbo stealing the election.
The big failure is eastern Congo where rebel movements, some of them connected to supposedly Western allies, Rwanda and Uganda, have caused mayhem in which rape and massacre are commonplace.
They left this ungoverned and difficult terrain to an expensive but so far ineffective UN force. Of all the conflicts that broke out at the end of the Cold War, eastern Congo has been the most intractable and ignored. Some cite 5.4 million deaths since it began in the early 1990s.
By all means destroy Assad's chemical weapons factory and put his airforce and army command centre out of action, but be ready to go in on the ground if this does not bring a quick victory for democracy and peace. Then put eastern Congo at the top of the list of the wars that must be ended.
Richard Dowden is Director of the Royal African Society and author of Africa: Altered States, Ordinary Miracles published by Portobello Books.