KHALED KAZZIHA NAIROBI, Kenya — Ethiopian Prime Minister Abiy Ahmed won the Nobel Peace Prize in 2019 for making peace with neighboring Eritrea. A year later, their armies joined forces against Tigrayan fighters in northern Ethiopia. Now the alliance has unraveled, raising fears of war between the former allies.

The confrontation threatens a region still recovering from the 2020-2022 war, which caused an estimated 500,000 civilian deaths through violence, famine and collapsed health services, according to researchers at Ghent University in Belgium.

A wider struggle over power, seaports and Nile waters links Ethiopia’s internal conflicts with rivalries stretching from the Red Sea to Egypt. Here is how the disputes connect.

Tigray is Ethiopia’s northernmost region, bordering Eritrea. The Tigray People’s Liberation Front, or TPLF, dominated Ethiopia’s government from 1991 until Abiy took power in 2018.

The 2022 Pretoria peace agreement ended the war between federal forces and the TPLF, but renewed fighting has effectively shattered it . Government-allied fighters entered Mekelle, Tigray’s capital, on Oct. 4, after the TPLF withdrew.

Abiy’s government announced a six-month caretaker administration to restore services, help displaced people return and prepare for elections. But losing towns does not prevent rebels from regrouping in rural areas, Magnus Taylor, an International Crisis Group analyst, said.

The TPLF joined six other opposition groups in September to try to overthrow Abiy’s governing Prosperity Party. The Ethiopian Peoples’ Forces Alliance for Survival includes the Amhara Fano National Movement and the Oromo Liberation Army, bringing together former adversaries.

Taylor told The Associated Press that the alliance combines political opposition to Abiy with military strength . Parallel military campaigns could stretch federal forces across several fronts, but whether the groups can pull it off remains unclear.

Tigrayan forces are divided. The government-allied Tigray Peace Force, comprising former members of the TPLF’s armed wing, is fighting alongside federal troops against the rebels.

Ethiopian authorities accuse the TPLF of seeking an alliance with Eritrea to destabilize Ethiopia, potentially bringing together enemies from the previous war. Eritrea denies backing the TPLF .

Ethiopia also accuses Eritrea of supporting insurgents and occupying Ethiopian territory, allegations the AP could not independently verify. Eritrea accuses Ethiopia of seeking to secure access to the sea by force.

Diplomatic relations have broken down . Ethiopia says it is acting in self-defense, while Eritrea described Ethiopia’s assertion that it was taking self-defense measures as a declaration of war.

The countries fought a border war from 1998 to 2000 that killed about 70,000 people, according to the U.N. peacekeeping mission established afterward. A prolonged standoff ended with Abiy’s rapprochement with Eritrean President Isaias Afwerki in 2018.

Eritrea was not part of the 2022 peace agreement in Tigray. Human rights groups and U.N. experts accused its troops of rape, looting and other wartime abuses. Isaias dismissed the allegations as “a fantasy” in 2023.

Abiy’s persistent calls for sovereign access to Eritrea’s Red Sea port of Assab have alarmed Eritrea and deepened the rift.

Ethiopia is the world’s most populous landlocked country, with an estimated 135.5 million people, but it relies heavily on neighboring Djibouti’s port for trade.

Abiy’s search for alternatives has also heightened tensions with Somalia. In 2024, Ethiopia signed an agreement with Somaliland , a breakaway region of Somalia, proposing a coastal lease for an Ethiopian naval base. Somaliland authorities said Ethiopia would recognize its independence in return.

The dispute helped draw Somalia closer to Egypt. The leaders of Somalia, Egypt and Eritrea pledged regional security cooperation in October 2024 , linking Somalia’s sovereignty concerns, Eritrea’s fears over its ports and Egypt’s dispute with Ethiopia over Nile waters.

Turkish mediation later secured an agreement for Ethiopia and Somalia to pursue commercial sea access under Somali sovereignty.

Egypt relies almost entirely on the Nile as a source of water for its population and agriculture and has called Ethiopia’s upstream dam an existential threat.

Ethiopia’s Grand Ethiopian Renaissance Dam , inaugurated in September 2025 on the Blue Nile near Sudan, is Africa’s largest hydroelectric dam. It is intended to double Ethiopia’s electricity generation capacity and support power exports. Ethiopia says it will not deprive downstream countries of their share of water.

A central dispute is how much water Ethiopia would release during a prolonged drought . Egypt and Sudan want binding rules for filling and operating the dam; Ethiopia favors guidelines. Sudan also wants coordination to protect its own dams.

Egypt and Sudan welcomed a U.S. offer in January to mediate the dam dispute , but disagreements extend to sharing the Nile’s waters more broadly. A separate Nile Basin accord took effect in 2024 , promoting equitable and reasonable use of the river. Ethiopia and five other countries backed it; Egypt and Sudan declined to sign, fearing their water shares could be reduced.

The danger is that Ethiopia’s internal fighting, its confrontation with Eritrea and regional disputes over ports and water could fuel one another. Taylor warned that the proximity of Ethiopian and Eritrean forces increased the risk of a wider conflict.