By Martin Plaut
Africa analyst, BBC News
The killing of African Union troops in Darfur underlines the critical situation in the Horn of Africa and beyond.
A new UN-AU force should deploy soon in Darfur
An arc of conflict stretches 3,000km from Somalia to the Central African
Republic posing a challenge the international community is struggling to cope with.
Five groups of international peacekeepers - in various guises - are trying to halt the fighting - and they are now joined by a new American military initiative, known as Africom.
Across the area, rebels are clashing with government forces, while peacekeepers attempt to contain the violence.
Arc of conflict
In the dusty streets of Mogadishu, Ethiopian troops are struggling to contain a fierce insurgency.
They are supported by a tiny African Union force.
Violence is a daily reality in Mogadishu
So far only Uganda has provided troops, and few other African nations show much appetite to back them up.
To the West, Ethiopia itself is fighting rebels on its own soil, in its eastern region - the Ogaden.
Further north, 200,000 Ethiopian and Eritrean forces are in places separated by just 80 metres along their contested border.
Ethiopia has threatened to tear up the peace agreement that ended their last war, increasing the possibility of a renewal of fighting.
Neighbouring Sudan is not only dealing with the crisis in Darfur.
The peace deal which ended its 20-year long North-South conflict is now also under strain and there have been rumblings or war here too.
The fighting in Darfur has spread westwards, spilling over into neighbouring Chad and the Central African Republic.
More than 100,000 Chadians alone have fled attacks from Darfur, and last week the UN Security Council mandated a French-led, European force to try to tackle the problem.
These crises are linked by a complex network of alliances.
For example, Eritrea backs the Somali insurgents, to reduce the threat on its border from Ethiopia.
Sudan is involved in the hostilities in Chad. So the crises feed off each other.
The United States has just increased its military influence on the continent.
The US has a military base in Djibouti
In the past it split responsibilities for Africa between its European and its Central Commands.
Now a new organisation, Africa Command, has come into existence.
Based, at first, in Germany, it is attempting to find an African base from which to operate.
But Africa has been less than receptive to the advances from Washington.
While Botswana is thought to be receptive to the idea, South Africa has been deeply hostile.
The African Union, never a powerful organisation, can do with help from almost any quarter in attempting to deal with the continent's multiple conflicts.
So far it has received some help from Nato and the UN on Darfur, but there is little appetite to intervene in Somalia.
The wider international community is so bogged down in Iraq and Afghanistan that it has little time to devote to Africa's perennial problems.
The result is immense suffering for the millions caught between these competing forces.