On Tuesday, just one day after Chad’s incumbent president, Idriss Deby, was declared the winner of the country’s April 11 presidential election, a military spokesperson announced that Deby had been killed on the battlefield while overseeing fighting with rebels known as the Front for Change and Concord in Chad, or FACT, in the country’s northern region.

Deby, 68, had been poised to claim a sixth term in office, having won almost 80 percent of the vote in an election victory most observers considered to be guaranteed in advance. He had led Chad since seizing power in a 1990 rebellion, making him one of Africa’s longest-serving leaders.

The Libya-based FACT rebels attacked a border post on the day after the voting and continued their offensive southward. Though the circumstances of his death remain murky, Deby, a former military commander and trained pilot, apparently headed to the front to oversee the heavy fighting.

Now, his death and the power vacuum it leaves behind has created political instability and uncertainty that risks rippling beyond Chad’s borders, across the Sahel and Lake Chad region. Parts of West Africa have faced years of insurgencies from Islamist extremists and armed groups affiliated with the Islamic State and al-Qaida, and Chad has been a key security partner in the multinational efforts to combat them.

In the hours after the announcement of Deby’s death, Chad’s borders were closed and a nationwide 6 p.m. to 5 a.m. curfew was imposed. Deby’s son, Gen. Mahamat Idriss Deby, was declared the interim president. He will lead an 18-month transitional council.

But despite the military’s attempt to project an orderly transition of power, the situation remains “extremely unstable and unpredictable,” said Richard Moncrieff, the Central Africa Project director at the International Crisis Group.

Mahamat, 37, who served as head of the presidential guard, will lead the country alongside 14 other generals until the end of the transition, the army said in a televised statement. But the FACT rebels have rejected the transitional council’s legitimacy and stated their intention of advancing to the capital, N’Djamena.

Moncrieff pointed to two important factors to watch as developments unfold. The first is whether the FACT rebels are able to join forces with other armed groups in the area before attacking. Deby has faced numerous insurgencies over the course of his rule, and any perceived weakness in N’Djamena could create incentives for other armed groups to band together.

“The other important question is whether the new military command under Deby’s son can command sufficient popularity to mobilize the army and push [the rebels] back and defend the nation’s territory,” he said.

Across the country, general dissatisfaction with the military’s assumption of power, which Moncrieff noted is unconstitutional, has been expressed by opposition political parties, civil society groups and trade unions.

This reflects “a popular mood in the country rejecting what they see as a continuity of a system which is dominated by the military,” Moncrieff said. “The perception [of Mahamat] is that he is part of that system.”

Moncrieff added that an immediate cease-fire with the rebels was urgently needed. Without one, he said, “a rebel advance on the capital could trigger a civil war.”

Despite the military’s attempt to project an orderly transition of power, the situation in Chad remains “extremely unstable and unpredictable.”

Chad’s political opposition and civil society groups have long accused Deby of repressive rule and corruption linked to the country’s large oil reserves. In 2003, Chad became an oil-producing nation with the completion of a $4 billion pipeline linking its oilfields to export terminals on the Atlantic coast.

Moncrieff described Deby as the leader of an authoritarian government that was deeply unpopular with many sections of the society. One reason he won reelection so handily earlier this month was because the ballot was boycotted by the major opposition parties.

Outside the country, however, particularly in Western capitals, Deby was seen as a strong ally in the fight against jihadist groups in the Sahel region.

French President Emmanuel Macron’s office released a statement saying, “France lost a brave friend,” and expressing “its strong attachment to Chad’s stability and territorial integrity.”

Deby maintained strong ties over the years to France, Chad’s former colonial power. French forces helped Deby fend off rebel offensives that threatened his hold on power on at least three occasions over the past 15 years. Chad’s capital now serves as a base for France’s Operation Barkhane, which has been battling armed groups in the Sahel since 2014. In February, Chad dispatched an additional 1,200 troops to support the roughly 5,100 French soldiers already deployed across the region.

Chad also supplies the most battle-hardened troops to the G-5 Sahel, a joint force comprising Chad, Niger, Mali, Burkina Faso and Mauritania that was established in 2017 in response to armed and violent extremist groups in the region. The force has strong financial and logistical backing from the French government, the United Nations, the African Union and the European Union.

In addition to his role in the Sahel, Deby was seen as a vital security collaborator in the effort to eliminate the Boko Haram terrorist group that originated in northeastern Nigeria but later expanded throughout the Lake Chad region. In recent years, a Boko Haram splinter faction has gained strength and branded itself as the Islamic State West Africa Province. Deby played a central role in the repurposing of the Multinational Joint Task Force comprising Chad, Nigeria, Benin, Cameroon and Niger to focus on the fight against Boko Haram after a series of attacks by the group in 2015.

Nigerian President Muhammadu Buhari expressed his deep shock at the death of Deby, whom he said “played a very active role in our regional joint collaboration in the military campaign against Boko Haram terrorists.” Buhari added that the current developments in Chad “will surely create a big vacuum in the efforts to jointly confront the Boko Haram terrorists and the Islamic State West Africa Province.” But he added, “We must now strive to mobilize even greater collaboration to defeat the terrorists.”

According to Mahamat Adamou, a Chadian journalist with long experience covering the region, Deby’s absence will have an impact on security and stability in the region because of how much “he has contributed to the fight against terrorism in the Sahel.” Adamou said the situation in the country is concerning and believes a peaceful transition is unlikely. “Deby’s son might cling to power like his father,” he added.

Moncrieff described the 18-month transition set by the military as “an extremely long time frame” for Chad at the moment, because of the ongoing possibility of a rebel advance on the capital.

“A democratic transition is extremely important, and it should be civilian-led,” he said. But he added that “this is extremely hypothetical at the moment because the situation is so unstable.”

The short-term priority, he said, is for international actors to help facilitate a cease-fire, while also seeking to negotiate a faster transition back to civilian rule. “This will help forge a consensus among political actors in the country in the context of stability,” Moncrieff said.