Carrot and Stick: Cuba
For half a century, the US attempted to destroy the Communist regime in Cuba with brutal sanctions which inflicted terrible suffering on the Cuban people but hardly any at all on Cuba's Communist leaders. During that time, most of the other Communist countries in the world moved sharply away from Communism and many of its brutal repressions. Why? Not because of sanctions or punishments, but because they could not resist participating in the benefits of market economies.
It's been obvious for many years that our sanctions against Cuba were counterproductive, not damaging the Castro regime but propping it up. We persisted in those policies because of the disproportionate power of a fanatical anti-Castro lobby of Cuban Americans. That generation is now dying off, and younger Cuban Americans have been paying attention to what worked with China, Vietnam, and other formerly hard-line Communist states.
That change made it possible for Obama to open the path to Cuba. Should we expect a rapid transformation? That's hardly likely. The old policy failed miserably for two and a half generations. The new is likely to take at least one. Is success guaranteed? Hardly, but five decades of abject failure mean that it's past time to try something else. There may be some slow movement while the Castros are still alive, but more likely real change will await a new generation.