One of the world's powder-keg countries faces a crunch test on Sunday when Democratic Republic of Congo heads into elections marred by delays, clashes and fears of polling-day chaos.The vote crowns two years of turmoil, sharpening worries that the fragile giant of central Africa may once more spiral into violence.Twenty-one candidates are vying to succeed Joseph Kabila, who aged just 47 has been at the helm for nearly 18 years.If all goes well, one will be sworn in on January 18 - the very first time that the DRC will have achieved a peaceful transition of power since gaining independence in 1960.But the prospects of achieving this have dimmed as concern over the poll's credibility has risen, along with a diplomatic storm with Europe.Sunday's election will be the DRC's first presidential ballot in seven years. It should have been held in 2016 when Joseph Kabila, in power since 2001, reached a two-term limit.But he remained in office, invoking a caretaker clause under the constitution.It came at the cost of protests that were bloodily crushed, leaving scores of dead.Then came a string of three election postponements - followed on Wednesday by a fourth delay in two regions hit by violence - and a storm over the introduction of electronic voting machines.The turbulence has revived traumatic memories of the DRC's bloodied past.On Wednesday, the presidents of Angola, Botswana, Namibia, Zambia and the neighbouring Republic of Congo called for "peaceful, free, democratic and transparent" elections and expressed deep concern at the violence.In 1996-1997 and 1998-2003, the DRC was the theatre of two terrible conflicts - the second of which was called "the Great War of Africa" for the millions of dead and homeless that it left.The conflict drew in countries from around central and southern Africa and its legacy lies heavily today on the east of the country, where militias fight over resources.Powerful trio The presidential elections - unfolding alongside legislative and municipal ballots - have a field of 21 candidates, with three men leading the pack. They are Emmanuel Ramazani Shadary, a hardline former interior minister; Felix Tshisekedi, head of the veteran UDPS opposition; and Martin Fayulu, a little-known legislator and former oil executive.But analysts also point to another power trio.None of their names are on the ballot sheets, but they are likely to wield much power behind the scenes regardless of who wins.One is Kabila himself, who personally selected the loyalist Shadary as his party's candidate - a choice that has invited speculation of a comeback the 2023 elections.The others are former militia leader Jean-Pierre Bemba, 56, and Moise Katumbi, 53, a wealthy businessman and former mayor of Katanga province.Both were barred from contesting the elections and are supporting Fayulu behind the scenes. Youth vote Two-thirds of DRC's estimated 80 million population are under the age of 25, which means that a "Kabila Generation" could have a huge say on polling day.Despite the many problems surrounding the election, many young voters interviewed by AFP said they would turn out, and economic reform was uppermost in their minds."We want things to change. We cannot live like this," said 24-year-old Kalumba Mwewa in Lubumbashi, capital of the mining province of Katanga.Mwewa said he trained as a mechanic but could not find work so instead earns a few dollars a day by illegally digging for copper and cobalt. He is considering voting for Fayulu."Maybe if I vote for him, it will change," Mwewa said.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.