By Martin Plaut
BBC African analyst
Sir Mark Thatcher's decision to plead guilty to participating - however unwittingly - in a coup attempt in the West African state of Equatorial Guinea has highlighted the ability of mercenaries to undermine African governments.
South Africa clearly wanted the coup plot to fail
The alleged plot involved South Africans travelling to Zimbabwe to pick up arms before travelling on to Malabo - the capital of Equatorial Guinea - to meet up with a group of fellow mercenaries who were already in place.
But the plot was soon exposed and backfired, with men now languishing in jails in Malabo and the Zimbabwean capital, Harare.
There was a time when a coup was the standard way of removing a political opponent in Africa.
During the years after independence in the 1960s, Africa saw no fewer than 186 attempts to overthrow heads of state.
A good number were launched from South Africa where the apartheid government was determined to use every lever at its disposal to fight against the end of white rule: first in the Portuguese colonies of Angola and Mozambique, then in Rhodesia (now Zimbabwe) and finally in South Africa itself.
It formed special battalions, known as "Koevoet" and the Buffalo battalion.
Drawn from across southern Africa they fought Pretoria's secret wars.
But when apartheid ended just over a decade ago, the new government was determined to put this bloody past behind it.
In 1998 South Africa passed a law forbidding its citizens from engaging in military activities beyond its borders without official permission.
"When the legislation was passed, little attention was paid to the welfare of the special forces who had been disbanded," said Angela McIntyre from the Institution of Strategic Studies in Pretoria.
This left a large group of former special forces troops with a lot of time on their hands, and few alternative forms of employment.
Many wound up in the dusty town of Pomfret on the edges of the Kalahari desert.
Some went on to act as security guards.
But when work in their old profession came along, they were open to offers.
Which is how 70 of them came to be on a plane bound for Zimbabwe - with an alleged final destination of Equatorial Guinea.
One thing is certain: the coup in which Sir Mark Thatcher was apparently involved was widely known.
South African President Thabo Mbeki warned both Zimbabwe and Equatorial Guinea that the plot was under way even before the plane left South African airspace.
South Africa clearly wanted the coup to fail, but not before it had exposed everyone involved.