Thabo Mbeki was left with a simple choice. Resign or face the full force of a party that no longer wanted him.
That the African National Congress (ANC) had seen enough was made clear at a news conference on the outskirts of Johannesburg...
The real reason: the repeated prosecution against Zuma...after a second court threw out the charges, the prosecutors decided to appeal the verdict, it was just too much...
So when Mbeki resigns, Parliament will elect someone to take his place until elections are held. Since Zuma is not a MP, he can't be chosen, but he can run in the next election and is expected to win.
As for Zimbabwe:
Zimbabwe's already fragile power-sharing agreement has lost both its architect and driving force.
The ANC says it is keen for Mr Mbeki to continue with his mediation role, but without the badge of office his influence and political clout will be much diminished.