Nearly two weeks of fighting in Sudan has threatened to tear apart the country of 49 million people - and to further inflame conflicts within its neighbors' borders.

Sudan borders seven nations - Egypt, South Sudan, Chad, Central African Republic, Libya, Ethiopia and Eritrea - each of which have faced war, violent civil unrest or political upheaval in recent years. As hopes for a swift resolution in Sudan dim with each failed cease-fire, a "catastrophic conflagration" of the conflict could consume the region, U.N. Secretary General António Guterres warned this week.

The violence in Sudan broke out April 15, pitting the Sudanese military against the rival paramilitary Rapid Support Forces after weeks of rising tensions over a power-sharing agreement.

The fighting has killed more than 450 people and displaced tens of thousands of civilians. Some have caught coveted seats on emergency airlifts and boats across the Red Sea. But most Sudanese have no option but to try to seek safety on their own.

The risk of a regional spillover is high given Sudan's geostrategic importance at the intersection of the Indian Ocean, Horn of Africa and Arab world. The Nile River and oil pipelines run through the mineral-rich nation, linking its fate with its neighbors.

From seven sides, Sudan's neighbors are watching with trepidation.

In the north, Egypt relies on Sudan as a bulwark against political upheaval and a partner in regional water disputes. Egypt is close with Gen. Abdel Fattah al-Burhan, the chief of Sudan's army and de facto head of state, who is battling rival Gen. Mohamed Hamdan Dagalo, better known as Hemedti, of the paramilitary RSF.

The Sudanese army and RSF joined up in 2021 to overthrow Sudan's civilian-led transitional government. The coup cut off Sudan's path toward democracy, which began when nationwide protests in 2019 forced out former military leader Omar Hassan al-Bashir after 30 years in power. Egyptians ousted their longtime dictator, former president Hosni Mubarak, in 2011; the military seized power in 2013 in a coup led by now-President Abdel Fatah El-Sisi.

Both water-stressed Egypt and Sudan rely on fresh water from the Nile River, which flows down from Ethiopia. The two countries say an upstream dam constructed by Ethiopia threatens their water supply - and any rift between Cairo and Khartoum could jeopardize efforts to reach a water-sharing agreement with Addis Ababa.

On Sudan's opposite side, in recent days thousands of mainly South Sudanese refugees have been streaming across the 1,200 mile-long border between the two once-warring nations, on a return trip to South Sudan.

War-weary South Sudan - one of the world's poorest countries - is ill-equipped to absorb Sudanese refugees or returning expatriates. About 12 million people live in South Sudan, roughly 2 million of whom are internally displaced and 75 percent of whom rely on humanitarian aid, according to Marie-Helene Verney, the U.N. refugee agency's representative for the country. About 2.3 million South Sudanese are refugees in other countries in the region.

The sudden influx of so many Sudanese and returning South Sudanese in recent days risks reigniting conflict and competition over scant resources in the young nation. The mainly African and Christian or animist South Sudan gained independence from Arab and Muslim-majority Sudan in 2011, ending decades of civil war. But in 2013 a civil war began again in South Sudan, fueled by unsettled ethnic divisions and feuding leaders.

The north of South Sudan is economically dependent on Sudan, and the fighting has disrupted supplies of critical food and goods. Aid agencies, at the same time, are stretched thin: The international humanitarian response plan for South Sudan has received less than a quarter of the funding it requires, Verney said.

On Sudan's western side, the United Nation's estimates that about 100,000 Sudanese will flee over the border to Chad, a key regional U.S. ally. About 20,000 people crossed into Chad from western Sudan's violence-plagued Darfur region in the first few days of fighting, according to the United Nations. Chad was already host to about 400,000 Sudanese refugees displaced by previous conflicts and housed in border camps.

The fighting in Sudan, and resulting power vacuums, could fuel political instability in Chad. Chad has a history of clashing with the precursor to the RSF - pro-government Sudanese Arab militias known as the Janjaweed. In the 2000s, the Janjaweed, under al-Bashir's direction, terrorized Sudan's Darfur region and conducted cross-border raids on Sudanese refugees in Chad. N'Djamena accused Khartoum of supporting Chadian rebels.

Chad also fears becoming caught in regional and proxy wars. Recently leaked U.S. intelligence documents, reported exclusively by The Washington Post, detail efforts by Russia's paramilitary Wagner Group to recruit Chadian rebels and train them in the Central African Republic in a plot to topple Chad's government. Wagner is active in the Central African Republic as part of Russia's efforts to gain ground in Africa, other leaked U.S. documents said.

The Central African Republic, a former French colony to Sudan's southwest, has been battered by years of rebellion, mismanagement and sectarian violence. Armed groups and militias effectively run the country, where half the population lacks enough food and very few have access to clean water, according to the United Nations. Already, the unrest has led to price increases.

Wagner and the RSF have allies in another of Sudan's neighbors: Several sources told The Post that a Libyan militia with Wagner ties sent supplies to Hemedti - allegations uniformly denied. Khalifa Hifter, a rebel leader who effectively controls eastern Libya, is backed by Wagner and is reportedly close with the RSF. Libya has been embroiled in civil war since the ouster of former dictator Moammar Gaddafi during the Arab Spring.

To Sudan's southeast, Ethiopia is eyeing how the fighting will affect two of its key concerns: Securing water rights for the Grand Ethiopian Renaissance Dam, and settling Ethiopian claims to a disputed border region where fighting has erupted before. Sudan has also been a refuge for tens of thousands of Ethiopians from the Tigray region, which fought a two-year war with the central government that ended in a shaky peace deal late last year - and threatens to flare up again.

Changes in the region's balance of power could also upset neighboring Eritrea's fragile alliances. Sudan has hosted thousands of refugees and asylum seekers from its eastern neighbor, and is the first stop for many Eritrean men fleeing the repressive government's forced conscription. Eritrea sided with Ethiopia in its recent war with Tigray rebels. Just a few years earlier, the two countries ended a decades-long cold war.

"The power struggle in Sudan," Guterres told the U.N. Security Council on Tuesday, "is lighting a fuse that could detonate across borders, causing immense suffering for years, and setting development back for decades."

The Washington Post's Claire Parker, Katharine Houreld and Rachel Chason contributed to this report.