To understand the implications of Benazir Bhutto’s assassination for Pakistan, first imagine what that country would look like without her Pakistan People’s party. It has been overwhelmingly a dynastic party and she was the last politically viable representative of the Bhutto dynasty. Without her to hold it together, it is highly probable the PPP will disintegrate.

In the short term, this is likely to benefit President Pervez Musharraf and the army but, in the longer term, Islamist extremists may have the most to gain.

If the PPP does fragment, the ability of the army to use patronage to put together coalition governments including some of these PPP fragments will be greatly increased. General Musharraf will also most probably gain more freedom of manoeuvre vis a vis Washington. American pressure on him will be diminished, for the US no longer has a strong pro-American civilian leader to promote in his place.

At a time when the US is becoming increasingly exasperated with Gen Musharraf’s administration – and Democratic leaders such as Barack Obama have been making openly menacing speeches – US options have become radically limited. Breaking with Gen Musharraf now means breaking with Pakistan as a whole, with potentially disastrous consequences for the “war on terror” and the conflict in Afghanistan.

Pakistan’s other former prime minister and opposition leader, Nawaz Sharif, may emerge as America’s protégé for want of anyone better. However, in Bhutto, Washington had a more appealing candidate who could be pushed into making an alliance with Gen Musharraf against Islamist extremism and support for the Taliban in Pakistan. No such alliance is possible with Mr Sharif, whom Gen Musharraf overthrew and imprisoned in 1999 and whom the president accuses of trying to kill him. Knowing that Gen Musharraf would not accept him as prime minister, Mr Sharif has repeated a call to his followers to boycott the parliamentary elections due next month, which may now be postponed.

However, Mr Sharif stands a much better chance of being prime minister again one day. He has strong support in northern Punjab and is the only remaining opposition leader with national stature. If at some point the army high command decides to force Gen Musharraf to resign and seeks to manage a transition to democracy, he would be the most obvious partner to approach.

For the other generals to do this, disorder and violence in Pakistan would have to become very much worse. Unfortunately, there is good reason to fear that this will happen as a result of Bhutto’s death and the likely disintegration of the PPP.

One obvious danger is in Sindh province, where clashes have already started. As a great Sindhi landowning family, the Bhuttos commanded the allegiance of many Sindhis; but as a family wishing to rule the whole of Pakistan, the Bhuttos were also careful to keep their appeal to ethnic feelings within bounds. They avoided appealing too strongly either to separatist sentiment or to hatred of the Mohajirs who, like Gen Musharraf, emigrated from India at independence and dominate the cities of Karachi and Hyderabad in Sindh. If the PPP disintegrates, there will be a much greater danger that Sindhis gravitate to purely Sindhi ethnic parties with bitterly anti-Mohajir agendas and that ethnic violence, separatism and tension among Pakistan’s different provinces will increase drastically.

Then there are the Islamists, who can be divided to some extent into the mainly pragmatic Islamist parties, which form the government of North West Frontier Province, and the Islamist extremists, some group of whom presumably killed Bhutto. Her death reduces a big Islamist fear, that of an alliance of the army and the PPP against them.

In the long run, the end of the PPP might also help the Islamist parties emerge as the only group with a claim to represent serious reform of Pakistan’s deeply corrupt and incompetent governing system. Ideally, this would lead to their transformation along moderate Turkish lines. But the presence of so many extreme elements, inflamed and strengthened by the war in neighbouring Afghanistan, means there is a real threat of hugely increased unrest – even US intervention and state collapse.

Pakistan needs a government of national unity, which would be backed by the army and which all the leading mainstream politicians would join. The prime minister should be a technocratic figure similar to Shaukat Aziz, who held the post until last month. The goals of such an administration would be to combat extremism and terrorism while presenting a firm front against US interference, and to continue the successful economic policies of recent years while distributing their benefits more widely. All should shun ethnic separatism and appeals to mass unrest.

Since holding Pakistan together is a vital western interest, such a government should receive strong backing from the west and should be used as a channel to develop negotiations with more moderate sections of the Taliban in Afghanistan.

Given the character of Pakistan’s political elites, this may seem like a hopeless pipe-dream. On the other hand, it is possible that they will have been shocked into greater sobriety and self-restraint by Bhutto’s assassination. This does, after all, represent a mortal threat to them all – as last week’s terrorist attack on Aftab Khan Sherpao, interior minister, also demonstrates. Pakistan’s mainstream politicians should now be able to see that if they do not work together, many of them will be assassinated separately.

The writer is a professor at King’s College London and a senior fellow of the New America Foundation in Washington. His latest book, ‘Ethical Realism: A Vision for America’s Role in the World’, co-authored with John Hulsman, is published in paperback by Vintage Books