The death of Ethiopian ruler Meles Zenawi creates another challenge to the region, which already has its share and more of instability.
Ethiopia's strongman leaves behind fragile East Africa status quo
In May 1991, reporters were summoned to the Berkeley Hotel in central London for what was billed as a peace conference to end Ethiopia's 30-year civil war. It was a small and rushed affair, and hardly lived up to its billing as the forum to end decades of bloodshed.
Within hours the two main rebel leaders, Meles Zenawi, of the Ethiopian People's Revolutionary Democratic Front, and Isaias Afewerki, leader of the Eritrean separatists, came up with a statement announcing they would enter Addis Ababa the next day and take power from the defeated military regime, known as the Derg.
They could have made the announcement themselves, but they gave it to the American mediator, Herman Cohen, to read out. It would carry more weight coming from him than from a couple of ragged Marxists from the bush.
The rebel leaders then set off - in a battered old Datsun, if memory serves - to return to Ethiopia and take power.
At the time, Ethiopia was a byword for famine and war. After 21 years of iron rule by Mr Meles, who died on Monday, it has a fast-growing economy and the status of a pillar of regional stability.
Mr Meles's relationship with Mr Isaias did not last. The latter led Eritrea, the part of Ethiopia which occupied its only access to the sea, to independence in 1993 and became its president. This led to two border wars over control of a barren strip of land and an enduring legacy of bitterness.
What happens to replace the vacuum left by Mr Meles is now the key question. He was a dominant figure in the crisis-ridden Horn of Africa, and a leader for the whole continent. An austere and unsmiling intellectual, he charmed foreign leaders from Bill Clinton to Tony Blair. Despite his Marxist beliefs, he realised that he had to cleave to the Americans, enjoying a close military and intelligence relationship with Washington.
He dressed up his concerns about the rule of Islamists in Somalia, and their support for ethnic Somali separatists in Ethiopia, in the language of the George W Bush's "war on terror", thus enjoying US support for Ethiopia's two invasions of Somalia. At the same time, he brutally crushed all political dissent at home, even jamming Voice of America broadcasts, which he considered seditious, while modelling his economic policies on Chinese state capitalism.
Whoever replaces him in the long term will struggle to manipulate the great powers with the same dexterity. The fear in western chancelleries is that the system he built up will collapse without him.
Officially, his system of rule was ethnic federalism - a multicultural federation based on ethnic and tribal representation. In fact this was a front for a one-party state, with real power increasingly concentrated in the hands of Mr Meles and his fellow Tigrayans, who are little more than 6 per cent of the population.
The former deputy prime minister and foreign minister, Hailemariam Desalegn, has been named as interim prime minister and will serve until 2015. But he is not seen as a powerful figure. Unless the leaders of the ruling party show the tactical flair of the late prime minister, it is easy to predict that the larger ethnic groups - the Oromo and Amhara - will seek to overturn Tigrayan domination, and that small local rebellions will grow.
The security forces appear strong and united. History will suggest that the Tigrayan elite would have to increase the level of repression to stay in power. But it is too soon at this stage to write off the system built up by Mr Meles.
What is certain is that his death comes at a delicate moment for the Horn of Africa. There are no strong governments in the region: fighting between the two Sudans, a year after their split, is an ever-present threat. Somalia is going through a difficult transition from anarchy towards a state. In Kenya, the spectre of the mass ethnic violence which ripped through the country in 2007 was revived this week by the massacre of 52 people near the Somali border. Across the Red Sea, Yemen is stuck in a stalled transition from the rule of Ali Abdullah Saleh.
The first focus is likely to be on Eritrea, where the death of Mr Meles could provide an opportunity to bury the hatchet. Eritrea is poor and increasingly friendless after the demise of the Qaddafi regime in Libya. But the mere disappearance of one of the brother-enemies who met in the Berkeley Hotel in London 21 years ago will not be enough: it would require sustained diplomatic support from the US and European powers.
Without that progress, stabilising Somalia will be harder. Ethiopia and Eritrea support different sides, with Addis Ababa keeping an estimated 10,000 troops in Somalia to fight against the Al Shabaab militia that Eritrea is accused of aiding.
Somalia has just elected a new parliament. A new president is to be elected soon, but despite the success of the African Union peacekeepers in driving Al Shabaab out of Mogadishu, there are doubts whether this is a real step to reviving the Somali state. It could be just a way of allowing a new cast of notables to bribe their way to getting their hands on foreign-aid flows.
The death of Mr Meles will not reduce Ethiopia's interest in Somalia. Having a large ethnic Somali population in its Ogaden region, the Ethiopian government will always be concerned about what is happening over the border.
What has changed is that the Americans have lost a stable ally in their counter-terrorism war at a time when other allies - such as Egypt - are in turmoil. If ethnic tensions in Ethiopia lead to a return of instability there, all bets on a Somali renaissance are off. And the judgement of all foreign powers who put their trust in Mr Meles will be more than ever questioned.
On Twitter: @aphilps