How Pope Francis played diplomat to help end US-Cuba cold war

The secret diplomacy that would upend a half century of enmity between the United States and Cuba was a year and half in the making.

It started with an American overture to Cuba and a series of nine meetings in Canada, beginning in June last year, according to senior administration officials.

The process involved an unusual intervention by Pope Francis, who opened the Vatican to help seal an agreement and wrote personal letters to President Barack Obama and Cuban President Raul Castro calling for a prisoner exchange and the resumption of diplomatic relations between the sides.

For a time, the talks stalled on definitions of who was a spy but ended on an emotional high note as three planes ferried released prisoners between the two countries in a choreographed swap.

The back-channel negotiations were conducted not by professional diplomats but by two of Obama's national security advisers, making it clear to the Cubans that the opening was coming directly from the Obama White House.

Along the way, administration officials from Secretary of State John Kerry on down used every opportunity to reiterate that the future of US-Cuba relations was entwined with that of American contractor Alan Gross, whose physical and emotional stamina seemed to be declining after five years in captivity.