Three major political groups have dominated Pakistani politics since independence - the military forces and the two political parties dominated by the Sharif and Bhutto families. All three are fully at play in the present political crisis there, as the military regime led by Gen Pervez Musharraf struggles to hold on to power in the face of mounting unpopularity and a more assertive civil society and independent media.
Yesterday's dramatic return to the country by former centre-right prime minister Nawaz Sharif, leader of the Pakistan Muslim League, lasted only a few hours, when he was arrested on corruption charges and immediately deported to Saudi Arabia. He had vowed to return from exile after the supreme court ruled last month that would be legal. Instead thousands of his supporters were arrested and rallies in his support were suppressed. He is determined to fight the issue through the courts on the grounds that he is fully entitled to stand in the forthcoming general elections and deserves support for that.
In a desperate effort to head off this prospect Gen Musharraf has been trying to strike a bargain with the exiled Benazir Bhutto, leader of the centre-left People's Party. He has denounced the corruption and incompetence of the successive democratic governments of the 1990s in which she and Mr Sharif alternated in power before they were both banished into exile by him in 1999. But he is now unable to survive without civilian help. Ms Bhutto says she will return to Pakistan later this month and is seeking a deal whereby she could become prime minister and Gen Musharraf remain president, but no longer in charge of the armed forces.
Since the military is so powerful, having ruled for more than half of the period since independence, it is very much an open question whether such a deal would be sustainable. Civilian rule has had to defer to the generals and intelligence services and their extensive networks throughout Pakistan's social and economic life.
But there are definite signs of change, symbolised by Gen Musharraf's failed effort to dismiss the chief justice this year and a burgeoning democratic movement to defend him. He faces huge problems in pursuing Taliban and al-Qaeda militants in the provinces bordering on Afghanistan, for which he has been supported by the United States. If he cannot reach an agreement with Ms Bhutto to stabilise his rule and hold elections other generals will be tempted to remove him. That is the logic of Mr Sharif's unceremonious expulsion yesterday. Pakistan stands once more at a political turning point between democratisation and military rule.