In a reconciliation that was long unthinkable, the two countries restored ties on July 20, 2015, 54 years after severing them in the aftermath of the Cuban Revolution.
The moment was marked by the reopening of Cuba’s embassy in Washington, followed by the official reopening of the US embassy in Havana four weeks later.
But don’t confuse diplomatic relations with friendship, cautioned former Cuban diplomat Jesus Arboleya.
“Cuba and the United States have never been friends and probably never will be,” he said.
The restored relationship is more like a “coexistence of opposites,” he added.
US President Barack Obama’s awkward visit in March to his Cuban counterpart, Raul Castro, sealed the rapprochement they announced in December 2014, but underlined the huge gulf still separating the countries despite the mere 160 kilometres between them.
Obama called for democratic reforms on the communist island, urged the regime to safeguard human rights and famously let his hand go limp when Castro tried to raise it in a victory salute at the end of a testy joint press conference.
A month later, Cuba’s communist party held a congress where it defied calls for greater opening, at which Castro condemned what he called external pressure “to end the revolution.”
His predecessor, older brother and revolutionary comrade Fidel Castro lambasted Obama’s visit, telling Cubans not to be taken in by the US president’s “syrupy words” and recalling the island’s long enmity with “the empire,” including Washington’s backing for the failed invasion of Cuba at the Bay of Pigs in 1961.
The main outstanding grudge is the financial and trade embargo the US has imposed on Cuba since 1962.
Obama has used executive power to chip away at it, but has failed to persuade a Congress controlled by his Republican opponents to scrap it entirely.
Cuba is also demanding the United States return its naval base at Guantanamo Bay, end policies that fast-track Cuban immigrants for US citizenship and pay it billions of dollars in reparations.
But despite the lingering tension, there are visible changes on the ground.
Cruise ships now sail from Miami to Havana. Travellers can stay at the Four Points by Sheraton, recently opened by American hotel group Starwood. And regular commercial flights between the two countries are due to begin in the coming months.
“It’s a very young process,” said Arboleya. But it started from “total divorce,” he added.
The former British ambassador to Cuba, Paul Hare, said both sides remain “wary” of each other.
“They know that every sign of ‘normality’ will be interpreted as a kind of ideological surrender,” he said.
“So they want to keep relations low-key and neither friendly nor antagonistic. Discussions on transport, the environment, security, etc. will continue to be the low-risk strategy.”
At a human level, the rapprochement has sent hordes of people across the Florida Straits in both directions.
Cubans, fearing an end to their preferential treatment in the US immigration system, are flocking there in larger numbers: Arrivals increased 78 per cent last year, to more than 43,000, according to the Pew Research Centre.
American visitors to Cuba have meanwhile surged 84%, despite the ban on tourism under the embargo.
In the United States, the question is how the November presidential election will impact the nascent thaw.
Both the Democratic and Republican parties’ presumptive nominees, Hillary Clinton and Donald Trump, have voiced support for the rapprochement, though Trump said the US should have made a “better deal.”
In Cuba, the question is how long it will take for reconciliation to boost an economy left adrift by the collapse of the Soviet Union and more recently the foundering of key backer Venezuela.
For Cubans, “the outcome has been a mixed bag,” said Michael Shifter, head of the Inter-American Dialogue research centre.
“This process has only served to reveal how deep Cuba’s political and economic problems go, and how complicated they will be to fix,” he said.