One of Congo’s most feared rebel groups declared an end to its violent insurgency Tuesday after a string of military defeats at the hands of Congolese army forces backed by a new U.N. combat brigade.

The conclusion of the M23 movement’s 20-month-long military rebellion injects a note of hope in the Central African country, where more than 5 million people have died of war-related causes since 1998. But it also highlights the many difficulties that must be surmounted before a sustainable peace can be achieved.

More than 40 militias and rebel groups still terrorize communities in Congo, which is roughly the size of Western Europe, and pillage its vast mineral wealth, including gold, tin and copper. Major grievances continue to fester among the country’s ethnic Tutsis, who formed the core of the M23 rebels. M23 political leaders had vowed that another Tutsi rebel group would rise up if M23 was defeated or if their demands were not met at the negotiating table.

‘Bumps in the road’

A crucial test is whether the government and the rebels, who are mostly disaffected Congolese soldiers, will be able to forge a political resolution, especially on sensitive issues such as amnesty and reintegration of the rebels into the national army. Peace talks in recent months have repeatedly stalled; a 2009 cease-fire that ended a previous Tutsi-led rebellion fell apart and led to the rise of the M23 insurrection in April 2012.

“It is a huge development for Congo, especially the people of eastern Congo, who have lived under M23’s control for the past year and a half,” Ida Sawyer, a senior Congo researcher at Human Rights Watch, said of Tuesday’s announcement. “But huge challenges remain.”

Nevertheless, the development was welcomed by Western and African diplomats who have worked for months to achieve an accord between the government and the rebels.

“Despite the bumps in the road, this is an important step in the right direction,” Russell Feingold, U.S. special envoy to Congo and the Great Lakes region, told reporters at a briefing in Pretoria, South Africa’s administrative capital, according to the Associated Press. “Everybody has to keep their commitments.”

The decision to lay down arms came hours after the Congolese government declared victory in the conflict, saying that its forces had pushed the rebels out of their last remaining outposts near the Ugandan border. The government offensive, which began nearly two weeks ago, swiftly ousted the rebels from more than a half-dozen towns that they had controlled for more than a year near the borders with Rwanda and Uganda.

African leaders at a summit in Pretoria had urged the M23 rebels to publicly declare that they would abandon the rebellion, a step that would pave the way for a peace accord with the Congolese government.

“The chief of general staff and the commanders of all major units are requested to prepare troops for disarmament, demobilization and reintegration on terms to be agreed with the government of Congo,” M23’s political leader, Bertrand Bisimwa, said in a statement. He said any grievances would be resolved through “political means only.”

Diplomats and analysts said they hope that the accord will not become a case of history repeating itself. On March 23, 2009, the National Congress for the Defense of the People, a Tutsi-led rebel movement known as the CNDP, signed a peace deal with the government that called for the rebels to be integrated into the national army. But the pact fell apart, and hundreds of soldiers, mostly former rebels, defected to launch M23, named after the date of the failed accord.

In November 2012, the rebels seized Goma, an eastern Congolese city with a population of more than 1 million, embarrassing U.N. peacekeepers. The rebels held the city for 10 days before voluntarily withdrawing under international pressure. One of their top leaders, Gen. Bosco Ntaganda, was wanted on war crimes charges by the International Criminal Court at The Hague. The United Nations accused him and other senior commanders of summary executions, rape and the use of child soldiers.

In the months after the siege of Goma, the rebels were riven by internal power struggles and disputes. They were significantly weakened earlier this year after Ntaganda turned himself in to the International Criminal Court in an apparent effort to flee the infighting.

Rwanda’s role

A key question now is Rwanda’s role. U.N. investigators have accused the Rwandan leadership — run, like the rebels, by ethnic Tutsis — of financing and arming M23, allegations that Rwanda has repeatedly denied. In recent months, U.N., Western and African diplomats have exerted heavy diplomatic pressure on the Kigali government to stop backing the rebels.

Feingold told reporters in Pretoria that he was confident that Rwanda would support the end of the M23 rebellion. He also added that rebels guilty of committing atrocities should not receive amnesty.

“Going forward, it is probably going to be much harder for Rwanda to back another abusive armed group in Congo,” said Sawyer, the Human Rights Watch researcher.

Sawyer added that senior M23 commanders must be arrested and brought to justice for committing war crimes and other atrocities. Equally, she said, Congolese soldiers should refrain from carrying out reprisal attacks against M23 fighters.

The end of the M23 insurgency follows the creation of a U.N. intervention brigade that has, for the first time in the world body’s history, an offensive mandate, tasked with combating Congo’s myriad militias. The force, which began operations in the summer, is not neutral and is openly backing Congolese government forces.

Among its next targets is the Rwandan FDLR rebel movement, made up of radical ethnic Hutus who fled Rwanda after the 1994 genocide, as well as moderate Hutus. Rwanda has long used the existence of the FDLR as a reason for interfering in Congo’s affairs. Other smaller militias rule other parts of eastern Congo, preventing Congo’s government from functioning there. Many control lucrative mining areas and are accused of committing numerous atrocities, including mass rapes.

Oxfam’s humanitarian program coordinator in Congo, Tariq Riebl, said Tuesday that although the M23 announcement marks a milestone, “the demise of one group doesn’t spell the end of conflict in the country’s east.”

“We mustn’t lose sight of the fact that there are many other armed groups still operating in this region,” Riebl said.