With mostly stagnant economies and stalled trade, South American leaders have had little to celebrate. So when they get together, as they did this week for the Mercosur trade summit in Argentina, what fills the gap are feel-good speeches about Latin camaraderie leavened with tub-thumping against gringo imperialism.

That script is about to change.

Argentine President Cristina Kirchner interrupted the speaker’s list to break the news of the agreement to re-establish diplomatic relations between Cuba and U.S., just then being unveiled in simultaneous announcements by Cuba’s President Raul Castro, in Havana, and U.S. President Barack Obama, in Washington. “For those of us with gray hair,” she said, “this is a historical moment.”

What may be most remarkable about the “historical moment” is that Latin American leaders were caught napping by the most significant pivot in the last half-century of Latin American diplomacy. Sure, Uruguayan President Jose Mujica had nudged Obama to make peace with Havana, and Washington-friendly Colombian leader Juan Manuel Santos had also weighed in.

Yet, apparently no Latin leader had a hand in the rapprochement other than Castro and Argentine-born Pope Francis, whose efforts Obama acknowledged in his speech Wednesday. (Canada reportedly also helped.) “We all thought this day would never come,” Brazil’s President Dilma Rousseff later admitted in a press conference.

That Latin inertia may be self-made. Cuba has long been a convenient stick for Latin America to wave at the gringos for moral advantage. Sure, its regime may have been a sclerotic dictatorship, propped up by the sort of rank repression and censorship that the rest of the hemisphere gave up decades ago.

One of my favorite Cuba stories comes from former Brazilian President Fernando Henrique Cardoso’s autobiography, “The Accidental President of Brazil.” It’s his on-scene account of a row at the 1999 Ibero-American summit, where wine-enhanced Latin leaders (Cardoso didn’t name names) dropped the hypocrisy and lit into Fidel Castro behind closed doors. “Damn it, Fidel! What are you going to do about this lousy, piece-of-sh— island of yours?”

But brothers Fidel and Raul Castro were neighborhood heroes, first for having pulled off a revolution under Washington’s nose and, second, for surviving Tio Sam’s best efforts to topple them.

The embargo was the dearest example of gringo arrogance, helping to keep the memories of Latin defiance alive and Che Guevara on the continental T-shirt. As dissident blogger Yoani Sanchez put it, “David can’t survive without Goliath.”

What comes next is unclear. The embargo is not over. Only the U.S. Congress can end that, and the newly energized Cuban-American caucus knows full well that “the opening changes the way the U.S. engages with Cuba, but it doesn’t change the Cuban regime,” as Eric Farnsworth, vice president of the Council of the Americas, told me.

That augurs ill for the eventual naming of a new U.S. ambassador to Havana, whom lawmakers must first vet.

Cuban dissidents seem relieved but underwhelmed. “What’s missing is a public timetable by the Cuban government in favor of democratization and respecting differences,” Sanchez blogged on Wednesday. “We can’t pop the corks yet.” Others are less skeptical. “Normalizing relations will take the air out of the argument that the U.S. is the source of all problems in Cuba and Latin America,” said former Brazilian foreign minister Luiz Felipe Lampreia.

Last week, Venezuelan President Nicolas Maduro was exhorting his fellow Bolivarians to take to the streets against the Yanqui menace after the Obama government threatened Venezuelan officials with “imperialist” sanctions.

By Wednesday, he couldn’t say enough about brother Obama, and his “gesture of greatness,” as he gushed at the Mercosur summit.

Of course, Maduro may also have just been doing damage control on what amounts to a strategic slap in the face. For most of the millennium, Venezuela and Cuba cultivated nearly carnal ties. When Hugo Chavez fell ill with cancer in 2012, Castro invited him to Havana for treatment. So tight were the jefes, there was talk of merging into a single country — Cubazuela, the wags called it.

Venezuela imported tens of thousands of Cuban snoops to beef up domestic surveillance and returned the favor to cash-strapped Cuba with tankers of cut-rate oil.

Now, with Chavez gone and Venezuela’s economy in disarray, Castro knows he needs another sponsor, companeros be damned.

“Two days ago, Maduro told Venezuelans to burn their U.S. visas,” quipped opposition firebrand Maria Corina Machado, on Twitter. “Meantime, Raul Castro was applying for his own.”

Adios, Cubazuela. Hola, Washington.

Mac Margolis is a Bloomberg View contributor in Rio de Janeiro.