The swearing-in of Morgan Tsvangirai as prime minister of Zimbabwe opens a new phase in the country that Julius Nyerere once described as "the jewel of Africa". In a continent plagued by fragile, failing and failed states, few cases show as dramatic a deterioration as Zimbabwe.

Considered among the brightest lights in sub-Saharan Africa on its independence in 1980 - at a function in which one of the stars was Bob Marley - it held its own for the first 15 years of independent nationhood. Its high educational and health standards, modern infrastructure and productive, largely agriculture-based economy made it into a power in southern Africa.

Fast forward to 2009. Ravaged by AIDS, life expectancy in Zimbabwe has dropped from 58 years of age in 1990 to 43 today. A cholera outbreak has infected 60,000, killed 3,400 and spilled over the borders to South Africa, Botswana, Zambia and Malawi. Some 83 per cent of the population live on less than US$2 a day, and many subsist on wild fruits and roots. Inflation, the highest in the world, is 230 million per cent, and a third of the population has fled the country.

National unity

What happened? How did Zimbabwe lose its way? Will Prime Minister Tsvangirai be able to do anything about it?

With its first Government of National Unity (GNU), between President Robert Mugabe's ZANU-PF and Tsvangirai's Movement for Democratic Change (MDC), Zimbabwe is replicating the Kenyan experience of "cohabitation" between President Mwai Kikwete and his erstwhile opponent, Prime Minister Raila Odinga. They have ruled together since April 2008, ever since Kofi Annan hammered out a deal to end the violence that gripped Kenya after the December 27, 2007 elections.

Launched in France in 1986 by then President Francois Mitterrand when he asked Opposition Leader Jacques Chirac to become his prime minister, 'cohabitation' demands a high degree of tolerance for radically different policy perspectives. It is the political equivalent of 'sleeping with the enemy'. The jury is still out as to how it has worked in Kenya, though it could be argued that the very fact the formula has survived its 10 months should be considered a success.

Will it work in Zimbabwe?

Founding father

One important difference with Kenya is that President Mugabe has ruled Zimbabwe since 1980, and is the country's founding father. And, the first indications are not promising. Cohabitation means the prime minister has real powers. Mugabe was not willing to give up the state security portfolios, and having two ministers (from different parties) in charge of the police, as is the case now, seems a design for disaster. Tsvangirai himself was reluctant to become prime minister, but was forced into it by the Southern African Development Community (SADC) heads, unwilling to countenance the Zimbabwean crisis any longer.

For the United Kingdom and the United States, the continuation of Mugabe in power is unacceptable. In an unprecedented step in diplomatic history, the British Embassy put an ad in a local daily indicating that Britain will not renew its aid to Zimbabwe as long as Mugabe is in government. Queen Elizabeth not too long ago stripped President Mugabe of his knighthood.

Things in Zimbabwe are bad, people are dying by the thousands, and the international community needs to step in. This is not easy. By law, international cooperation funds need to be exchanged at the official rate at the central bank. This means they subsidise the Government, since the official exchange rate is only a minimal fraction of the 'real' (meaning black market) one. But the underlying problem is a deeper one.

Many would argue that the main reason Zimbabwe's situation has deteriorated so drastically over the past decade has been Mugabe's willingness to do whatever is needed to keep himself in power, even if it means running his country into the ground. Yet, the driving force behind this stubbornness goes beyond strict megalomania. There are other reasons why Mugabe is leery of leaving power.

The existence of the International Criminal Court and the principle of universal jurisdiction for human rights violations imply that the dictators of this world are no longer safe. General Augusto Pinochet's arrest in London in October of 1998, the first time a former head of state was detained abroad for crimes committed at home, and the subsequent indictment of President Slobodan Milosevic by the Special Tribunal on Crimes in the former Yugoslavia - another first, this time for a sitting head of state - broke new ground in international human rights law. This is a welcome development, and the world is a better place as a result of it. But, there is a problem.

Unwilling to step down

One reason it is said Mugabe is unwilling to step down (although, about to turn 85, he knows very well the clock has run out) is because of what happened to Charles Taylor, Liberia's former strongman. Under international pressure, Taylor resigned from the presidency in August 2003, to go to Nigeria, where he was offered safe exile. Yet, in March 2006 he was released by Nigeria, to be tried in Freetown by the Special Court for Sierra Leone. Taylor, one of Africa's worst and bloodiest warlords, is now in prison in The Hague, facing 11 charges of crimes against humanity.

I remember only too well visiting Harare in November 1998, shortly after Pinochet's arrest in London, and, while staying at the Meikles Hotel, listening to an hour-long programme on BBC-Africa about the implications of that arrest for Africa. There was a panel of commentators from different countries, and listeners phoned in from all over the continent with some passionate reactions.

The knotty question of what will happen to dictators the morning after they leave State House needs to be addressed if we want them to leave of their own volition.