A rebel militia known as M23 has seized the key Congolese city of Goma, threatening displaced civilians and raising fears of a broader regional war.

Some 400,000 people have fled their homes in eastern Congo as the rebels advanced on Goma, according to the U.N. refugee agency. In the last few days, many more have arrived in the city.

M23 is funded and directed by the government of Rwanda, according to the United Nations and the United States. Rwanda denies any direct involvement with the group.

The conflict has its roots in Rwanda’s 1994 genocide, which spilled over the border into Congo, leading to decades of fighting. Like the leaders of Rwanda, M23 is mostly made up of people from the Tutsi ethnic group.

What is M23?

M23 is one of more than 100 militias roaming the mineral-rich areas of eastern Congo. But the group stands out from the rest because of its territorial gains and its control of the area’s lucrative mining industry.

“They pose much more of a threat to Congo than any other armed group,” said Judith Verweijen, a researcher with 15 years of experience in eastern Congo who teaches at Utrecht University in the Netherlands.

The group’s name refers to its claim that the Congolese government failed to honor an earlier peace agreement, signed on March 23, 2009.

The leaders of M23 claim the group is in eastern Congo to protect fellow Tutsis and other speakers of the Kinyarwanda language from persecution by the Congolese authorities.

The United Nations has repeatedly warned against widespread hate speech against Tutsis in eastern Congo and said last year that risks of genocide and atrocity crimes in the region remained high. Eastern Congo also harbors hundreds of suspected perpetrators of the Rwandan genocide who haven’t been brought to justice, it said.

The group was founded in 2012 and quickly captured Goma for the first time, before withdrawing after global leaders pressured Rwanda. It lay dormant throughout most of the 2010s before resuming attacks on the Congolese Army in 2021.

Who is backing M23?

M23 is under the military command of Sultani Makenga, a Congolese rebel who fought in Rwanda in the 1990s, joined the Congolese Army in the 2000s, and then defected to join M23 in 2012.

Mr. Makenga receives instructions and support from the Rwandan Army and from Rwandan intelligence services, according to United Nations experts and Congolese and Western intelligence agencies.

Rwanda has denied any direct involvement. It also claims that Congo’s reinforced military presence in the east threatens its security, and that the region has harbored members of the Hutu ethnic group who were behind the genocide of 1994.

Experts say that Rwanda, a country smaller than Massachusetts with limited natural resources, is seeking to expand its sphere of influence and plunder mineral resources in eastern Congo.

What are the origins of M23?

After the 1994 genocide, about a million people from the Hutu ethnic group fled Rwanda for Congo, then called Zaire. Among them were many genocidaires, responsible for killing millions of Tutsis. In 1996, Rwanda invaded Congo, and backed the rebellion that eventually led to the downfall of Congo’s longtime kleptocratic leader, Mobutu Sese Seko.

Several groups were created in the late 2000s to defend Tutsis in Congo and fight the Congolese army, including M23’s predecessor, the National Congress for the Defense of the People. On March 23, 2009, the group signed a peace agreement with Congo and agreed to integrate its fighters into the national army.

That deal fell apart in 2012, when hundreds of former rebel soldiers mutinied within the Congolese army and formed the M23 movement.

In 2013, after Rwanda stopped funding the group under intense international pressure, the Congolese Army and U.N. peacekeepers defeated M23.

It has been on the offensive ever since it re-emerged in 2021.

What’s new this time?

Experts see a few major differences from M23’s 2012 offensive.

Territory: M23 now controls twice as much land as in 2012, according to Bintou Keita, the United Nations’ top official in Congo. The territory under its control increased by 30 percent between April and November last year. As rebels have seized more territories, sexual violence has been rampant and injuries sustained by heavy artillery have skyrocketed.

Capacity: M23 has over the past year accelerated recruitment, both voluntary and forced, including minors. Its fighters have used weapons never before seen in eastern Congo, according to U.N. experts, such as anti-tank missiles.

Rwandan troops: United Nations experts said in a report least year that up to 4,000 Rwandan troops had been deployed in North Kivu, M23’s main area of operations, surpassing the number of M23 fighters.

What is M23’s endgame?

According to the United Nations, M23 is planning for “territorial expansion and the long-term occupation and exploitation of conquered territories.”

In April, the group seized Rubaya, home to one of the world’s largest mines of coltan, a key component in the manufacturing of smartphones. M23 has issued mining permits and formed a “state-like administration” for mining production, trade and transport, according to U.N. experts, with profits of more than $800,000 a month.

The minerals are eventually routed to Rwanda, according to reports documenting the trade from M23-controlled territories to Congo’s neighbor.

In 2012, M23 pulled out of Goma after Rwanda withdrew its support to the group. Western donors later applied diplomatic pressure on Rwanda, cutting much-needed aid. This time around, the same powers have only used words to condemn the offensive.

“Rwanda might be testing the waters to see what it can get away with,” said Ms. Verweijen. “That will shape how the M23 insurgency is going to unfold from now on.”