While each country in Southern Africa has its own politics, recent developments involving presidents provide interesting contrasts across the region. Which presidents gain and lose power in 2018 - and how they do so - will have significance for the region as a whole, not least in helping determine its continued stability.
As 2018 begins, Joseph Kabila is clinging to the presidency of the Democratic Republic of the Congo (DRC), claiming that there is insufficient funding to hold an election, amid growing protests against him in Kinshasa and elsewhere. It remains to be seen if he will fulfil the undertaking he has made that elections will be held in December this year.
Other countries in the region start 2018 on a much more promising footing. In Botswana, President Ian Khama, approaching the end of his two presidential terms, is expected to step down in an orderly succession in April and will be suceeded by the vice-president.
In both Zimbabwe and Angola autocratic presidents who had been in power for almost four decades lost power in 2017 in very different ways.
Military intervention in Zimbabwe
In the case of Zimbabwe the country's army intervened in November 2017 to force Robert Mugabe to give up power. This came after he had, under the influence of his wife Grace, sacked Emmerson Mnangagwa as vice-president. The Southern African Development Community did not need to intervene, and even the mediation mission it planned wasn't required.
Instead, the Zimbabwe military acted, with the ruling party, Zanu-PF, to replace Mugabe with Mnangagwa. It did so peacefully, denying during the entire process that a coup was underway. The 93-year-old Mugabe, in office since 1980, initially refused to step down, but was finally removed both as president of the country and of the ruling party.
The country will go to the polls in mid-2018, and Mnangagwa, who was confirmed in December 2017 as Zanu-PF's presidential candidate, has said that the election will be credible, free and fair, but he has yet to confirm that he will allow international and other observers.
With the military more obviously involved in government than anywhere else in the region, Zimbabwe's opposition parties divided, and with Morgan Tsvangirai, leader of the Movement for Democratic Change Alliance seriously ill, there is little likelihood that Zanu-PF or Mnangagwa will lose power.
In Angola José Eduardo dos Santos, suffering from ill-health, agreed in early 2017 to step down as president of the country. He nominated a man he thought would be a trusted successor, hoping to continue to wield influence as president of the ruling MPLA.
After elections for the National Assembly in August, João Lourenço duly succeeded Dos Santos as president. To widespread surprise, he began sacking the heads of some of the country's key institutions. These included Dos Santos's daughter, Isabel dos Santos, who was CEO of the state oil company Sonangol.
And in early 2018 her brother José Filomeno dos Santos, was removed as head of Angola's sovereign wealth fund. Their father's influence was rapidly slipping away.
In Angola, as in Zimbabwe, a change of leader to one with a more reformist approach probably means that the ruling party has consolidated itself in power.
In South Africa in December 2017 the leadership of the governing African National Congress (ANC) passed from Jacob Zuma to Cyril Ramaphosa, who thus became heir apparent to the presidency of the country. While there is no two-term limit for ANC presidents, Zuma had brought the ANC into discredit and Ramaphosa, despite having worked closely with Zuma as deputy president, was seen as the one who would curtail the corruption and "state capture".
For now, Zuma remains president of the country until general elections due to be held by June 2019. The country waits to see whether, how and when Ramaphosa can arrange to take over as president of the country as well as of the ruling party.
A presidential challenge defeated
In Namibia, Hage Geingob had to meet a challenge to his continuing as leader of Swapo, the governing party, in November last year. He was, however, confirmed in his position and will therefore be Swapo's presidential candidate for the election scheduled to take place in November 2019.
Geingob supporters now fill all the key posts in his government, enabling him to make policy as he wishes. This is very different from South Africa, where the new ANC leadership remains divided and where Ramaphosa, when he becomes president of the country, will find it difficult to adopt new policies.
Malawi and Zambia
Malawi must hold elections in 2019 and the contest for the presidency then has already begun. It is not known whether Joyce Banda, the former president and leader of one of the country's leading political parties, will return from self-imposed exile abroad to stand again. In 2017 she was formally charged with having been involved in the massive "Cashgate' corruption scandal" that was uncovered while she was president.
In Zambia, by contrast, where the next election is not due until 2021, the question is how Edgar Lungu, who took over the presidency after narrowly winning the presidential election in August 2016, will try to consolidate his power.
In 2017 Lungu became more authoritarian. Hakainde Hichilema, the leader of the main opposition United Party for National Development, was arrested on what were clearly trumped-up charges. These were only dropped in August after interventions by the Secretary-General of the Commonwealth and inside Zambia by the local Catholic Archbishop.
Too often developments in one country are seen in isolation from similar ones elsewhere. Given that South Africa is the most important country in the region, how the Ramaphosa-Zuma poser is resolved will be significant for the region. Elsewhere, how presidents gain and lose, and try to consolidate their power, will help shape the continued stability of the region.
Will political tensions be managed internally, as in Zimbabwe in late 2017? Or will they require some kind of intervention by the Southern Africa Development Community, in the DRC and perhaps elsewhere, to prevent them from escalating? Throughout the region, contests for presidential power are likely to keep political passions on the boil.