In what could be a historic moment for Zimbabwe, President Robert Mugabe and Mr. Morgan Tsvangirai, head of the opposition Movement for Democratic Change (MDC), have signed a power-sharing agreement.

Under the agreement, Mr. Mugabe will cede some of his power for the first time since becoming president. While this paves the way for a national government that could end the economic and humanitarian crisis that constitutes daily life in Zimbabwe, success depends on real power sharing. Regardless of how desperate the situation appears, there is no guarantee that this effort will succeed.

Mr. Mugabe has ruled Zimbabwe with an iron fist since the country claimed its independence in 1980. Once a resistance hero, Mr. Mugabe has become another petty tyrant, crushing all opposition to his rule and turning what was once the breadbasket of southern Africa into an economic basket case. Inflation now tops an annualized 11 million percent (the official estimate); some independent analysts put it at 40 million percent. The vast majority of Zimbabweans live on subsistence rations and millions more have fled to neighboring countries.