The country rejected China and embraced Washington and Europe to help build a $250 million rail corridor that will channel cobalt, copper and other critical minerals out of Angola and its neighbors, diversifying U.S. supplies of raw materials critical to the green revolution. Angolan and American officials hope it will spark a broader economic boom, and the U.S.-funded Export-Import Bank has committed to a $900 million loan for a U.S.-made solar panel project along the rail line, the bank’s largest-ever investment in that kind of installation in Africa.

Angola’s foreign minister also publicly declared to his Russian counterpart last year that he was concerned about the start of “World War III” as the result of the war in Ukraine, sharp words for a longtime major backer.

Biden administration officials say Angola’s warming relationship with Washington is a win for both countries and a model for economic cooperation with nations that have at times felt neglected by the United States or portrayed as pawns in bigger geopolitical maneuvers. They characterize the turnaround in Angola as an especially positive sign of the United States’ appeal as a partner in Africa and across the developing world.

“We see America’s future and Africa’s future as joined,” Blinken said Thursday in the Angolan capital, Luanda, where the waves of the Atlantic lap at the shores of a city whose skyscrapers jostle with pastel-colored remnants of Portuguese colonial rule.

The United States and Angola’s “relationship is stronger, it’s more consequential, it’s farther-reaching than at any point in our 30-year friendship,” Blinken said during the capstone of a four-day trip to sub-Saharan Africa that he made even as the Biden administration juggles crises in Gaza and Ukraine. Angolan President João Lourenço visited Biden in the Oval Office in November.

Biden administration officials bristle at the notion that they are engaged in a geopolitical competition with China and Russia over Africa, saying that even if those rivals weren’t active, Washington would be building the same ties on the continent. They say that the Cold War-era frame is not a helpful way of thinking about relations and that African countries need not face a binary choice between the United States and Beijing or Moscow.

“They want to have a diversity of partners, right? They don’t want to be entirely dependent on China. And they honestly don’t want to be entirely dependent on us,” said a senior administration official, speaking, like others, on the condition of anonymity to talk frankly about U.S. diplomacy.

“Our rivalry with China doesn’t define our relationship with Africa, but it’s not divorced from it,” the official said. In these meetings, “that’s part of what we do, but it’s one aspect of it.”

Instead, they say, partnership with the United States can deliver jobs for Angolans and Americans, diversify a supply of critical minerals that is overly reliant on China, and boost U.S. climate objectives by promoting renewable-energy projects.

Angola fought a bitter war of independence from Portugal that turned into a 27-year civil war in 1975, after the country threw off colonial rule. The Soviet Union and Cuba backed the ruling government. During the Cold War, Washington supported the opposing forces. The conflict tore the country apart and left deep-seated suspicion toward the United States from José Eduardo dos Santos, who led the country for 38 years before he stepped down in 2017. Under his rule, the country was known for being among the most corrupt in Africa.

The resentment toward Washington created fertile ground for countries such as China to come in and offer to finance massive infrastructure projects, including a rail line across much of the country to connect Angola’s Lobito port with the resource-rich inland. The project was completed in 2012 and was built largely by Chinese workers who flew in for the construction and departed afterward. China has loaned more money to Angola than to any other country in Africa.

The rail project didn’t turn out as planned. Equipment was faulty, and China was slow to fix it. Dos Santos’s handpicked successor, Lourenço, has opened the door to looking beyond the country’s traditional partners.

When Angola started considering an expansion of the project a decade later, officials rejected a Chinese bid and opted for a 30-year concession to a U.S.-backed consortium to rebuild and extend the lines and operate the rail service. Construction took place last year, and the first shipments of minerals traversed Angola this month. U.S.-made steel for the bridges needed for the rail line created hundreds of jobs in the United States, project backers say.

The Angolan and American partners say they eventually want to extend the line, which they have called the Lobito corridor, eastward to the Indian Ocean. They say it would spark an economic boom in a region short on roads and rails. Already, European and international investors have piled on top of the U.S. efforts, offering agricultural and industrial projects along the new rail line.

The economic cooperation has deepened relations between the former antagonists in Washington and Luanda, as Angolan leaders have played an important role in mediating a conflict in the neighboring Democratic Republic of Congo and have been more willing to stand up to Moscow and Beijing, including the warning to Russian Foreign Minister Sergei Lavrov about World War III.

“It’s mutually reinforcing,” another senior Biden administration official said, describing what partnering on infrastructure projects has enabled in Angola. “We have a really deep diplomatic partnership with them, which we didn’t have in the past. We’re working really seriously with them to address the problems in eastern D.R.C.”

“People want to talk to us, want us to be involved in helping them solve their problems,” the official said. “And that’s nice. I’m not sure you see necessarily that with some of their external partners.”

Angolan leaders say they welcome the partnership with the Biden administration.

“All partnerships that can fit into our needs and our policy in terms of our developmental policy are welcome,” Angolan Foreign Minister Téte António told reporters after meeting with Blinken.

As for the criticism he delivered to Russia over its invasion of Ukraine, he said that “we believe as Angola that the best friends are the ones who tell the truth,” he said. “We had to warn our friends.”