When South Sudanese President Salva Kiir joins Africa's not so exclusive rebels-turned-leaders club on Saturday, he will find his new state dependent on similar men for trade, investment - and survival.
Oil-producing South Sudan is due to declare independence on July 9 - a split approved in a referendum promised in a 2005 north-south peace deal to end two decades of conflict.
For former rebels in neighbouring countries, such as Ugandan President Yoweri Museveni and Ethiopian Prime Minister Meles Zenawi, the equation is simple.
A prosperous and peaceful South Sudan will mean billions of dollars in trade and investment for those two countries and also for East Africa's Kenya, Tanzania, Rwanda and Burundi.
A return to war, or significant violence, with the north, will be a disaster for the revenues of every country in the region and could mean an influx of refugees.
Mr. Meles told Reuters in an interview the latter option was a "ghastly" prospect, and analysts say east and Horn of Africa nations are doing all they can behind the scenes to prevent it, knowing that the new state will not be viable without their backing.
"South Sudan will, for the foreseeable future, need its neighbours in East Africa more than they need it," said J. Peter Pham, an analyst with U.S. think-tank the Atlantic Council.
"In addition to relying on Uganda and Kenya for outlets to the outside world, South Sudan will also depend on Ethiopia, for security and likely for electrical power."
South Sudan is Uganda's main export market, importing goods worth $184.6-million (U.S.) in 2009, according to the Uganda Exports Promotions Board. Kenyan exports to South Sudan were worth $157.7-million the same year.
A return to war could cost South Sudan's neighbours as much as 34 per cent of their combined annual GDP over a 10-year period and could cost Kenya and Ethiopia $1-billion a year, according to a report by Frontier Economics.
"Meles has brokered negotiations in Addis for obvious reasons," an Ethiopian Foreign Ministry official said. "None of us can afford that sort of loss but, more than that, we're going forward with power exports and South Sudan will be a customer."
Though three-quarters of Sudan's 500,000 barrels a day of oil are produced in the south, its only way of exporting it is through the north's pipelines.
"This requires co-operating with Khartoum and this probably also means paying a premium for the privilege," Mr. Pham said. "The only alternative would be to build a pipeline which would link to the one that will likely be constructed in Uganda."
South Sudan said on Wednesday it planned to build a link to a pipeline in Kenya.
In the short term, the south will depend on both East Africa and the north, but moves such as building a pipeline link to Kenya or newly oil-producing Uganda are the sort of swings away from the north that analysts expect in the longer term.
"South Sudan now looks like the most likely candidate if the East African Community is enlarged to include countries beyond the five current member states," said Joseph Lake, an analyst with the Economist Intelligence Unit.
The East African Community (EAC) numbers Kenya, Uganda, Burundi, Tanzania and Rwanda and is moving forward with plans for closer integration and a single currency.
Analysts say EAC membership would give South Sudan immediate clout against its former masters in Khartoum and would improve its security.
Stronger security is vital, as the north and south have yet to demarcate their border and agree how to share oil revenues. The north's army and fighters linked to the south have clashed in Southern Kordofan, the north's main oil state.
Most analysts don't see a return to all-out war as likely, and say the new state's survival will be threatened more by corruption in its ruling Sudan People's Liberation Movement (SPLM) and by ethnic divisions within its own borders.
"How the SPLM manages to deliver internal security and meet some of the expectations that come with independence are crucial," said Angelo Izama, a regional security analyst with the Uganda-based think-tank Kwote.
But if conflict were to reignite, analysts say Ethiopia - the main military power in the Horn and a key Washington ally - would, with backing from East Africa, support the south as it has done in the past.
"Together with the United States and other Western countries, the states of east Africa are most responsible for the birth of South Sudan as a nation," Mr. Pham said.
"In fact, long before Western countries became involved, Ethiopia, Kenya and Uganda provided safe haven and support for the SPLM," he said.
It has also not been lost on the countries upstream of the Nile that Khartoum's traditional backers, Egypt and Libya, are now floundering.
"Everybody's playing nice diplomatically right now," a Western diplomat in Kampala told Reuters. "But there's no mistaking east Africa's loyalty - it's with Salva."