The country's first post-war elections were held in 2006, but the vote highlighted a deep east-west divide along ethnic and linguistic lines. Furthermore, many observers say continuing violence in more remote areas could destabilize the peace process and re-ignite the regional war that officially ended in 2003.

The largest U.N. peacekeeping force in the world is stationed in Congo, with 17,000 troops, and the International Criminal Court in The Hague has launched investigations into war crimes. But it's a Herculean task keeping control of a country the size of western Europe and lacking the most basic infrastructure. Jungle paths or rivers are often the only routes. Dozens of heavily armed groups - some of them still reportedly backed by influential politicians or foreign governments such as Rwanda and Uganda - stoke ethnic rivalries and vie for control of valuable natural resources.

Rwanda and Uganda officially withdrew their troops from Congo in 2002 and 2003, and although they are often accused of keeping a foothold in Congo through proxy militias, much of the violence in the northeastern border regions originates in the power vacuum left behind when their armies pulled out.

A HUMANITARIAN CRISIS

Militias regularly target civilian men, women and children, and thousands of families are on the run for their lives. Some 5.4 million people have died since 1998 from violence and war-related illness, according to studies by U.S.-based aid agency International Rescue Committee, which says fighting frequently prevents people from seeking out what scant health services are available. "Congo is the deadliest conflict anywhere in the world over the past 60 years," said Richard Brennan, IRC's health director.

Aid agencies say rape is endemic in regions where militias go on the rampage and live by brutalizing villagers for food and loot, and the very old and the very young suffer the worst. "(I've seen cases) from a six-year-old girl to a 75-year-old woman," said Jason Stearns, senior analyst for central Africa with International Crisis Group. "Rape has become part of a culture of violence... The traditional moral structure of society is falling apart."

More than 340,000 Congolese are scattered across the region, although some are starting to go home. The U.N. refugee agency, UNHCR, said at least 15,000 people returned during 2007, mostly from Angola, Rwanda and Sudan. And it was expecting another 72,000 would go back during 2008. Almost 1.4 million people are displaced within the country's borders, according to UNHCR, and waves of violence means more are still regularly uprooted from homes, at least for short periods of time.

Aid experts regularly cite the crisis in Congo as the most underreported emergency in the world. "It's the worst humanitarian tragedy since the Holocaust," John O'Shea, chief executive of Irish relief agency GOAL, told AlertNet. "The greatest example on the planet of man's inhumanity to man."

HOW THE WAR STARTED

Congo was formerly known as Zaire - a name given it by President Mobutu Sese Seko, who ruled the country with an iron fist and a greedy purse from 1965 until his overthrow in 1997. The origins of Congo's war are intimately connected to the 1994 genocide in neighboring Rwanda, where some 800,000 people from the minority Tutsis and political moderates from the majority Hutus were slaughtered at the instigation of the extremist Hutu government. Rwanda's post-war Tutsi government invaded Congo in 1996 to pursue extremist Hutu militias that had crossed the border, in the process helping Congolese rebels end Mobutu's 32-year rule.

 Rwanda installed rebel leader Laurent Kabila as president but then turned against him when he started stirring hatred towards Tutsis in Congo. Rwanda intervened to try to remove Kabila, but he fought them off with assistance from Angola, Namibia and Zimbabwe, while Uganda weighed in on the Rwandan side. The ensuing regional war raged from 1998 to 2003.

After Kabila was assassinated in January 2001 his son Joseph took power and began negotiating peace. He set up a temporary power-sharing government with four vice-presidents, two of them from former rebel groups, and then won presidential elections in 2006. Although Kabila is popular in the Swahili-speaking east of the country, he's viewed as an outsider by many people in Kinshasa and the west, where Lingala is the main language.

 Kinshasa politicians, local bigwigs and neighboring countries are accused of cashing in on valuable natural resources in eastern Congo, and international rights activists say Rwanda and Uganda continue to arm and fund militias in the area even after pulling out their national troops.

THE GOVERNMENT, ARMY AND UNITED NATIONS

President Joseph Kabila and his Alliance for the Presidential Majority won presidential elections in 2006, the first time in 40 years the country had freely gone to the ballot to vote for a leader. The election year was marred by sporadic violent clashes between Kabila followers and supporters of his main rival, Jean-Pierre Bemba, who remains convinced the international community had Kabila lined up for the job already.

The government is hobbled by endemic corruption and analysts say there's still the risk that politicians sidelined by elections could voice their opposition in street protests and violence rather than the political arena.

Congo's new army is meant to unite tens of thousands of former gunmen who fought with a plethora of armed groups, but soldiers are ill-disciplined, poorly fed and don't have proper equipment, according to Belgian-based think tank International Crisis Group.

British-based aid agency Save the Children said in December 2007 that militias were increasingly recruiting children - often from schools - to fight or act as porters, spies and sex slaves. The charity said it helped 800 child soldiers demobilize in 2007.

Save the Children estimates some 1,500 children still remain active in army brigades, local militias and foreign rebel groups. Human Rights Watch says they're often hidden from observers or coached to say they're over 18.

 Army living conditions are appalling, without barracks or canteens, let alone health services, and experts say their salary is not a living wage. As a result, soldiers often resort to taxing and abusing the local population. In the east of the country, government soldiers have fled their posts rather than fight against militias and villagers have reported being attacked by the national army as well as other gunmen. "(The) army is still the largest human rights abuser in the country," Crisis Group said in a 2007 report.

 The United Nations first sent a mission to Congo - MONUC in 2000. It was initially small and weak, but by 2006 had almost 17,000 troops, making it the largest U.N. peacekeeping force in operation. Peacekeepers have been dogged by accusations of sexual exploitation of women and children. They have also been accused of smuggling gold in exchange for guns. A 38,000-strong national police force has been deployed around the country, but Crisis Group said it was concerned training focused too much on crowd control and not enough on ordinary policing skills such as criminal investigation, making statements and procedures for dealing with sexual violence.

MILITIAS, NEIGHBOURS AND INTERNATIONAL COURT

Although many former rebels have given up their guns or joined the national army, others are still resisting the integration process and continue to fight over resources, territory or ethnic grievances. It is hard to keep up with the shifting loyalties of various armed groups operating in Congo and their leaders, some of whom have been backed at various times by Rwanda or Uganda but later switched sides. And sometimes rival militias join forces to take on the national army.

Then there are militias called Mai Mai, who model themselves on traditional warriors, touting talismans that they say make them invincible and terrorizing villagers.

Fighting occasionally follows ethnic divisions, frequently stirred up by politicians both in Congo and outside, since some Congolese tribes have affinities with Hutus or Tutsis in neighboring Rwanda and Burundi.

A number of Congolese warlords and militia leaders are awaiting trial at the International Criminal Court (ICC) in the Hague. The trial of militia leader Thomas Lubanga for war crimes was due to be the court's first but the case was suspended in 2008 after the prosecution withheld documents. Other detainees include former Congolese rebel warlord and vice-president Jean-Pierre Bemba who is charged with leading a campaign of rape and torture.

CONGO HOTSPOTS

North and South Kivu

Renegade general Laurent Nkunda - a former commander of the main rebel group that controlled the eastern part of the country, the Rwandan-backed Congolese Rally for Democracy (RCD), rejected conciliation with the government right through the 2006 election period. He then started integrating his 4,000 well-trained troops into the national army in February 2007, but the delicate relationship has regularly broken down.

A Tutsi born in North Kivu, Nkunda says he wants to stay in the area in order to protect fellow Congolese who speak Kinyarwanda, a language of Rwandan origin. Local Tutsis from South Kivu are known as the Banyamulenge.

The RCD initially united Hutus and Tutsis in North Kivu, where both tribes speak Kinyarwanda. Rwanda denies continuing to support Nkunda, whose group is now called the National Congress for the Defence of the People. Violence flared at the end of October 2008 when Nkunda launched a new rebel offensive, advancing on the provincial capital Goma. The fighting has caused massive displacement. Foreign governments are pressing President Kabila and Rwanda's President Paul Kagame to revive a deal under which both pledged to take steps to end the rival Tutsi and Hutu rebellions.

 An estimated 200,000 hungry, frightened civilians are crammed into camps outside and around Goma. Sleeping out in the open, some even wrap themselves in banana leaves at night to find some protection from the cold. Tens of thousands more are feared to be roaming North Kivu's bush-covered hills, desperately seeking safe shelter, food and water.

 The United Nations and foreign aid groups are scrambling to cope with an emergency described as "catastrophic" by relief workers. They are rushing to distribute supplies and provide medical care for the displaced, but fighting has disrupted aid operations.

North Kivu's long-suffering civilians have been clamoring for more protection, not just from Nkunda's rebels, but also from marauding army soldiers and Mai-Mai militia who have killed, looted and raped.

Anti-corruption campaign group Global Witness says the armed factions in North Kivu, including Congo's army, are using the province's cassiterite, gold and coltan to gain profits and perpetuate the violence, abetted by willing buyers.

"For as long as there are buyers who are willing to trade, directly or indirectly, with groups responsible for grave human rights abuses, there is no incentive for these groups to lay down their arms," Global Witness director Patrick Alley says.

 Ituri

The mineral-rich northeastern district of Ituri was basically under Ugandan control throughout the war. Thomas Lubanga, leader of the ethnic Hema-dominated Union of Congolese Patriots (UPC) militia, was the first suspect at the International Criminal Court (ICC), accused of recruiting children during the UPC's occupation of the eastern Congolese town of Bunia between August 2002 and March 2003.

Two warlords from the other side of the Ituri conflict, Germain Katanga and Mathieu Ngudjolo, are accused by ICC prosecutors of war crimes and crimes against humanity including murder, sexual slavery, rape, inhumane acts and recruiting child soldiers.

Katanga, also known as "Simba", or lion, led the Patriotic Forces of Resistance of Ituri (FRPI), while Ngudjolo headed the allied Front of Nationalists and Integrationalists (FPI) militia.

Clashes in 2003 were divided more or less between opposing militias from the Hema and Lendu ethnic groups. Human Rights Watch tracked who was who in Ituri's armed groups in 2003. Land disputes between the Hema, who are pastoralists, and the Lendu, who are farmers, were exploited by leaders of armed political groups vying for influence in the region. Both have, at different times, been backed by Uganda. However, the traditional Hema-Lendu ethnic dispute is no longer the driving factor behind violence in Ituri. Both groups now fight together to protect their control of the region against the government and United Nations.

The region calmed down, but U.N. peacekeepers were accused of colluding in an April 2006 attack on civilians in Kazana, Ituri. Fighters in several Ituri militias have started demobilizing or integrating into the army, but it's a process which could easily be overturned, analysts say.

Katanga

Violence in Congo's most mineral-rich province is driven by tensions between the region's north and south, between natives and perceived outsiders, and between the army and ex-government militias called Mai Mai who have run amok and now extort money from civilians. Hundreds of women have been raped, according to the U.N.'s Office for the Coordination of Humanitarian Affairs, which said many people took refuge on islands formed by clumps of papyrus plants floating on lakes in Katanga's Upemba National Park.

U.N. troops are spread thin on the ground in a region the size of France, according to a 2006 report Katanga: The Congo's Forgotten Crisis, by International Crisis Group.

Katanga, the home province of President Joseph Kabila, has a long history of unrest, much of it provoked by wealth in mines that once produced 50 percent to 80 percent of the national budget. It was the site of a secessionist war in the 1960s, and Katanga's politicians have been accused of trying to break away in more recent years.

Orientale

Lord's Resistance Army (LRA) rebels, who have terrorized northern Uganda for two decades, crossed into the northeastern province of Orientale during 2005, and one of their camps was discovered in Garamba National Park. Eight Guatemalan peacekeepers were killed in January 2006 when the United Nations launched a special operation to capture LRA Deputy Commander Vincent Otti. Otti, who was indicted for war crimes by the International Criminal Court, was killed by his own allies in late 2007.

Bas-Congo

Followers of Bundu dia Kongo (BDK) reject central authority over the western province of Bas-Congo and are campaigning for the re-establishment of the pre-colonial Kongo kingdom, which encompassed parts of present-day Angola, Democratic Republic of Congo and Gabon. More than a hundred people died in a January 2007 crackdown on the BDK, and dozens more died when police tried to assert state control in March 2008.

There's little U.N. presence on the ground, since more than 90 percent of its troops are in the east, and rights campaigners are worried about innocent civilians getting caught in the crossfire. "Whenever the government goes out against the BDK, they go all guns blazing," Anneke Van Woudenberg, a senior researcher for New York-based Human Rights Watch, said.

RESOURCES, COLONIALISM AND THE COLD WAR

Many analysts categorise Congo's conflict as a "resource war" motivated by control over eastern Congo's rich natural deposits of gold, diamonds, copper, cobalt, timber and cassiterite, a tin ore. Mining of coltan, a conductor used to make cellular telephones, increased instability in eastern Congo when it boomed in 2000. Rwanda and its army profited from the trade, according to researchers at British-based advocacy organisation Global Witness.

When the bottom fell out of the coltan market in 2001, producers switched to cassiterite, often found in the same places. The tin ore is used in lead-free circuit boards for electronic equipment and its rising value was heavily influenced by China's phenomenal economic growth. World consumption of cassiterite climbed by 14 percent in the first half of 2004, Global Witness said. "The Chinese demand for tin made the world price skyrocket," said Stearns of Crisis Group.

Cassiterite miners earn $4-6 a day, well above the $1 a day most miners can expect to take home, according to a Global Witness report. The mining industry is unregulated and dangerous. During the coltan boom of 2000, so many people abandoned farming to work in the mines that there were shortages of the local food staple, manioc flour.

Profits from Congo's resources have historically been extracted by whoever controls the soldiers at the mine gates, making demilitarization unattractive to those with bank accounts on the receiving end, including politicians in Kinshasa.

Western security sources are worried that Congo's lax security could be exploited by countries such as Iran to get their hands on uranium which might be used for nuclear programs. Congo provided the uranium for the U.S. atomic weapons dropped on Japan in 1945, and its Shinkolobwe mines are in unstable Katanga province.

Mobutu - who ruled the country for 32 years - diverted enormous quantities of wealth into his own bank accounts, much of it from copper mines in Katanga. He built up a fortune while the state was deprived of funds to build infrastructure and services for the general population.

After nationalizing foreign-owned mines in the mid-1960s, Mobutu encouraged local entrepreneurs - usually his friends and relatives - to take charge of guarding their own territory, setting the pattern for the present day. Historians say Mobutu was following in the footsteps of Belgian colonialists, who forced huge swathes of the population to work on rubber plantations that funded lavish palaces for the Belgian monarchy. Colonial administrators instituted a brutal system of slavery, demanding employees account for every bullet used with the hand of the slave who had been shot. The hands were smoked to preserve them, according to historian Adam Hochschild.