For opponents of the 84-year-old Gabriel Robert Mugabe, the campaign of violence meted out by pro-government militias begs a crucial question. Either it is history repeating itself - the latest episode in a long catalogue of brutality leading, inexorably, to a rigged election and another lease on power for his ossified regime; or this latest assault on opposition supporters marks the last chapter in the long and blood-soaked struggle for democracy in Zimbabwe, and the threshold of a new era.

Nobody can predict with certainty the outcome of the looming presidential election - not even the malleable Zimbabwe Electoral Commission, which dithered for almost a month before announcing the results of the inconclusive first-round ballot on 29 March. And for all his ruthlessness, Mugabe craves a legacy as the man who gave Zimbabweans back their land: it is far-fetched, but not inconceivable, that he would defy the tightly knit Joint Operations Command (JOC) - a council of political, military and intelligence chiefs which is the real centre of power in Harare - and concede defeat.

More plausibly, his regime will endeavour to cling on, fearful of the consequences of any concession. Zimbabwe's government is paralysed by a shortage of hard currency, and the productive economy is in ruins. But amid widespread hunger, a parallel economy persists in the resilience of small traders. A third of the population depend on remittances from the diaspora, while a well-connected lootocracy wring eye-watering profits from the unlikely opportunities of hyper-inflation. For anyone else it makes most sense to leave, as a third of Zimbabweans have done since 2000.

The country they leave behind is gripped by momentous struggles. For the first time in recent years, both factions of the divided Movement for Democratic Change have signed up to an electoral pact. The united opposition commands an unprecedented majority in parliament. Morgan Tsvangirai has survived bitter infighting and a succession of strategic blunders to emerge as the undisputed popular challenger to Mugabe.

Ministers have so far ignored the MDC majority in parliament, but its presence will become significant once the real power brokers in the JOC begin to contemplate a successor to Mugabe. Hopes that a consensus-seeking candidate might emerge from the ranks of Zanu-PF, a fashionable notion in political circles in Harare, have been diffused. A presidential bid by former finance minister Simba Makoni drew only 7 per cent of the popular vote.

Zimbabweans, wracked by cynicism, have grounds to believe that opposition politics, although painful, may at last be possible and useful. Nothing like this has happened before, although the old cliché of a region helplessly detained by its history is far from the truth. The historical relationship between Zanu-PF, sponsored during the colonial era from Beijing, and its pro-Soviet counterparts among the mass movements of southern Africa, has always been vexed. Today, at last, Mugabe can no longer claim his brothers are behind him.

The so-called quiet diplomacy of South African president Thabo Mbeki is not yet abandoned. But a widely leaked letter to Mbeki from Tsvangirai, in which he asks Mbeki to excuse himself from the regional mediation, confirms a relationship in need of repair. Mbeki's efforts to engage the regime in Harare have been much criticised, but his rapport with Mugabe is arguably much worse. Zimbabwe's president has often reneged on agreements with the South African leader, sometimes even before Mbeki's plane had left Harare. But Mbeki's mediation, under the auspices of the 14-nation Southern African Development Community (SADC), enabled a more credible first round election than many observers had feared.

Those gains are clearly in jeopardy, as violence escalates in the run-off campaign and aid agencies have been banned. The MDC claims 65 of its supporters have been killed and many hundreds beaten in attacks orchestrated, ultimately, by the veteran Zanu-PF securocrat Emmerson Mnangagwa. A report published last week by Human Rights Watch claims Defence Forces commander General Constantine Chiwenga and police chief Augustine Chihuri have been tasked with terrorising MDC supporters, particularly in Zanu strongholds.

The violence is symptomatic of a lack of any alternative strategy within Zanu. Mnangagwa, 61, is the closest thing to a genuine Mugabe loyalist, and aspires to succeed him as president. But Mbeki's mediation has left an obstacle in his path. A constitutional amendment, No 18, ratified by the Harare parliament last year, vests the power to appoint a presidential successor between elections in members of parliament.

Former Zambian president Kenneth Kaunda has called for a unity government, arguing that neither side will be able to claim a workable mandate after 27 June. Amendment 18 at least provides a basis for some kind of power-sharing between the Joint Operations Command and a cross-party grouping of elected parliamentarians. The constitution is vulnerable, of course, to the whims of the ruling party. But the looming presidential contest may yet mark the start of a more protracted negotiation over Mugabe's successor.

Kaunda wants Mugabe as president and Tsvangirai as prime minister. The MDC angrily rejects the job descriptions. But if and when Mugabe steps down, there is a kind of logic in the call for power-sharing. First round results - broadly endorsed by independent surveys - gave Zanu-PF a narrow lead in the overall tally of votes, although the ruling party lost on parliamentary seats and Mugabe trailed Tsvangirai in the presidential ballot. Much will depend on the swing voters who backed Simba Makoni. Diplomats from South Africa, Britain and the US are said to have encouraged him to stand, a measure - if true - of the gulf between diplomats' thinking and the popular vote. Makoni's supporters have doubts about Tsvangirai, but few are likely to support Mugabe.

Beyond Zimbabwe, the impact of its collapse on the wider economy of southern Africa has long been a concern for neighbouring governments. Mugabe's defiance of the liberalising economic agenda at the core of the new policy initiatives - from the African Union to Nepad, the unfortunately named New Partnership for Africa's Development - weighs heavily on regional ambitions. The SADC needs Zimbabwe's industrial infrastructure and educated population to advance the cause of regional economic integration.

African critics

Mugabe has often belittled his African critics and questioned their liberation credentials. Although he retains some support from Angola and Namibia, the influence of neighbouring countries is limited. But on a recent visit to London, Jacob Zuma - who replaced Mbeki as leader of South Africa's governing ANC in December - referred to Tsvangirai as "Morgan", in pointed contrast to "President Mugabe" (or closer to home, "Mbeki"). Mugabe's refusal to attend the last SADC summit in April in Lusaka - to which Tsvangirai was invited - confirms he has lost interest in African institutions. International opinion has proved still less effective. The United Nations has made no impact in Zimbabwe. Kofi Annan's intervention to encourage an inclusive government in Kenya is a substantial precedent, but still far from a model for others to follow. G8 resolutions for Africa are undermined by a failure to agree a common international position on Zimbabwe.

At base, the problems of diplomacy cannot be separated from the suspicion - on both sides - that foreign policy is determined by unreconstructed notions of racial solidarity. This charge, levelled in the west at African leaders, must be applied also to the "liberal" western democracies.

The collapse of the post-colonial pact between Mugabe and his erstwhile enemies - the Rhodesian farmers, Britain, capitalism and Empire - has triggered a keen appetite for historical vindication among western critics. Mugabe's fiercest critics are often the same people who, in the early 1980s, turned a blind eye to the notorious "Gukurahundi" slaughter of 20,000 Ndebele loyal to his rival, the late Joshua Nkomo. But in Zimbabwe today there is not much appetite to indict Mugabe for human rights abuses - if only he would go quietly.

The real reckoning between politicians and securocrats in Harare is still to come. Meanwhile, the Cold War has ended, and apartheid is defeated. Our own Gordon Brown wants Britons to take pride from their colonial heritage. Mugabe is equally sincere in his belief that, on the day of judgement, he will be admitted to heaven ahead of the warmongering George Bush and Tony Blair.

Mark Ashurst is director of the Africa Research Institute. Gugulethu Moyo is a Zimbabwean lawyer who works on southern African issues for the International Bar Association