Most of the international observers I spoke with believe that Abiy’s soldiers and the Eritreans have committed violence on a greater scale than the Tigrayans, but none of the partisans in the conflict seem to have avoided brutality. A recent U.N. report described war crimes and human-rights violations on both sides. In addition to the widespread starvation caused by the siege, Abiy’s forces and allies had killed and raped civilians, and carried out scores of air strikes on civilian targets, including one on a displaced-persons camp in which some sixty civilians died. The Tigrayan forces, the report said, had committed “large-scale killings of Amhara civilians, rape and sexual violence, and widespread looting and destruction of civilian property.” The senior Western official told me, in disgust, “They’re all as bad as each other.”

On one of my trips with Abiy, he brought along his predecessor, Hailemariam Desalegn, and I pressed him on the war in Tigray. Hailemariam chose his words carefully, describing the conflict as “complicated.” The T.P.L.F., he argued, was like other liberation movements that had seized power and held it: “They can’t conceive of not being in control anymore.” Hailemariam suggested that the besieged Tigrayans had no way out but to fight: “Eighty per cent of their people depend on the government for support, and there is a lack of food. The youth are turning to banditry, robbing trucks. The T.P.L.F. don’t have any resources to help the situation.” He added, “What the Tigrayans do have is a big army, and a lot of people willing to die. Dying is their only solution.”

For Abiy, Hailemariam was perhaps his most significant link to the previous government. Yet Abiy disparaged him, over lunch at the palace: “He never expected to be P.M. He was picked because he was from a minority, and both the Tigrayans and the Amhara wanted someone without a constituency they could control.”

With the conflict deepening, Abiy also seems to lack a substantial constituency of his own. Abraham Belay, a Tigrayan who is Abiy’s defense minister, said that he had struggled to negotiate with both sides. “I have been trying my best to become a middleman,” he said. But the Amhara extremists rejected him for being a Tigrayan, and the Tigrayan hard-liners called him a banda, a traitor. “There are people who don’t want this to calm down,” he said. “Some are Tigrayan and Amhara extremists. And there are Oromos, too, who are killing Amharas and also other Oromos.”

The senior U.S. official explained that when Abiy and the Tigrayans agreed to a truce, in March, it was under pressure from the Americans. Each side had its own interests in mind. “The government of Ethiopia wanted reëngagement with the West, mostly for economic reasons, and the T.P.L.F. because of the humanitarian situation,” the official said.

Abiy seems cornered. He can’t get Western money without reconciling with the Tigrayans—but, even if he wants to make peace, his Amhara and Eritrean allies won’t agree to it. The Eritrean President, Isaias Afwerki, would be a formidable enemy for Abiy; at seventy-six, he is one of the most ruthless and determined political survivors in the world. In mid-September, a report from the Swedish consulate in Asmara noted that the Eritrean People’s Army had summoned all active members to report, “without discrimination of age or background or health status.” It added that anyone who failed to report would “suffer consequences including their residential houses being closed, family members being thrown out of their houses, family members being detained.”

Other forces are massing, too. The Tigrayans have evidently mobilized all of their available fighters. Mulugeta, the former T.P.L.F. member, estimated that the Ethiopian government had assembled as many as half a million troops in the region; other reports suggest that Abiy has commandeered Ethiopian Airlines flights to move recruits to the front.

Last week, a large Eritrean force crossed the border into Ethiopia. Reports from the region describe intense fighting on at least five fronts. “What’s happening here is a civil war,” the senior Western official told me. “I believe there’s a totally compelling logic not to fight, but they’ll do it anyway.”

On the Blue Nile, two hundred miles from the Tigrayan border, is Abiy’s most consequential project: the Grand Ethiopian Renaissance Dam, a five-­billion-dollar behemoth that is the largest hydroelectric facility on the African continent. It has been under construction since 2011, and when it is complete, in two and a half years, it will transform life in Ethiopia.

Approaching it from the nearest airstrip, you come first to a secondary dam, which extends for three miles across an otherwise untouched jungle valley. Not far upstream, the main dam is squeezed between two great hills: a concrete wall nearly five hundred feet tall, with the river spewing through in a roiling wash of muddy water.

When I visited, the project manager, an amiable engineer, reeled off statistics. When the dam is finished, it will contain 10.7 million cubic metres of concrete, making it “more than three times the size of Hoover Dam.” Beyond the dam, an immense reservoir was filling, gradually submerging a string of jungle mountains; it will eventually be fifty miles wide and a hundred and fifty miles long. In the massive structure where the turbines are embedded, billboards on the walls were emblazoned with slogans: “African Pride,” “History in the Making,” “Unity.”

The dam project began under the T.P.L.F.; Debretsion Gebremichael, who now leads the insurgency from Mekelle, was in charge. But Abiy has made it his own, and it has been a tremendous source of national pride. Millions of ordinary citizens helped pay for it; in Addis, every construction worker and schoolteacher seems to have made a contribution. The dam has also received essential support, including engineering and infrastructure, from Europe and from China. (Hailemariam Desalegn, who was the Deputy Prime Minister as the project got under way, suggested that he preferred aid that came without conditions: “We like the Chinese way of doing things, because they don’t say, ‘Do this, don’t do that.’ ”) All around the structure, workers in jumpsuits and hard hats hustled from job to job, on foot and in giant trucks.

Even before the conflict with Tigray began, the dam was inflaming regional tensions. Sudan and Egypt rely on the Nile for most of their water, and they fear that the dam will limit their supply; there were skirmishes at the border and bellicose warnings from Egypt, which has Africa’s most powerful military. Abiy insisted on going ahead. “No force could stop Ethiopia from building a dam,” he said. “If there is a need to go to war, we could get millions ­readied.” Construction is now nearly complete. Thirteen enormous turbines are being tested before they are switched on; during my visit, the second was about to go online. When the dam is complete, it will double the electrical capacity of Ethiopia, where half the citizens now have no access to power.

Abiy is betting that the dam, and the scores of other projects he has instituted, will one day seem like the culmination of a great plan, in which the war is just a distraction. In his book, he advocates “striving to make a new today, rather than being stuck in the past.” But Berhane Kidanemariam, the former diplomat, suggested that Abiy was merely stumbling from one contingency to the next. “I don’t think he really is trying to help one ethnic group or the other,” he said. “He doesn’t have a strategy. He wants to be seen as a reformist, but he is not. Power and money are what motivate him. He isn’t even really anti-T.P.L.F. When he attacks them, he just uses it as an instrument.”

On one of my visits to the palace, Abiy told me that his real motivation was to aid his neediest citizens. “I am for poor people,” he said. “If I can save the life of a thousand poor people, that is the reason, not to see good news on the BBC, or whatever.” Despite all the strife in the country, he was certain of his place in his people’s hearts. “When I leave office, I am one hundred per cent sure—one hundred per cent sure—that millions of Ethiopians will cry,” he said. “They will not say, ‘Oh, we are happy he left.’ You will see it. People will see what I left.” ♦