Alan Gross was the obstacle that would not be moved: the American contractor whose imprisonment kept relations between the United States and Cuba locked in place, as paralyzed as a seized transmission.

Now, in both Washington and Havana, the obstacle has been removed, and the rusty gears of Cold War diplomacy have begun to move.

Mr. Gross’s release on Wednesday, along with the release of another person held in Cuba and three convicted Cuban spies held in the United States, amounts to a collective break from more than 50 years of distrust, anger and inertia. Though President Obama and Raúl Castro, the president of Cuba, will find their own ways to describe what they have done, it is clear that they have both taken a chance on pursuing reconciliation.