The long and extraordinary political career of Fidel Castro is over - at least as far as the presidency is concerned. But his enormous influence will live on. His regular columns for Granma, the state newspaper - which he has continued to write throughout his illness - will continue. Only the strapline will be altered: instead of the reflections of the commandante en jefe, now it will be plain old camarade Fidel. For Cubans and international observers alike, they will still bear close reading.

There can be no replacement for Fidel. Not simply because of his qualities as a leader, but because the historical circumstances will never be the same. Castro has lived through everything from the Cuban revolution to the fall of the USSR, and decades of confrontation with the US. The fact that he departs while alive will help to ensure a peaceful transition. The Cuban people now accept that the country can still be run the same way by a different team. For a year and a half they have been getting used to the idea, while Castro remained theoretically president but his brother, Raul, held the reins. It was Fidel the mentor, as ever.

The most surprising thing that I found out about the man, in the hours we spent together compiling his memoirs, was how modest, human, discreet and respectful he was. He has a tremendous moral and ethical sense. He is a man of rigorous principles and sober existence. He is also, I discovered, passionate about the environment. He is neither the man the western media depict, nor the superman the Cuban media sometimes present. He is a normal man, albeit one who is incredibly hard working. He is also an exemplary strategist, one who has led a life of enduring resistance.

He contains a curious mixture of idealism and pragmatism: he dreams of a perfect society but knows that material conditions are very difficult to transform. He leaves office confident that Cuba's political system is stable. His current preoccupation isn't so much socialism in his own country as the quality of life around the world, where too many children are illiterate, starving and suffering from diseases that could be cured. And so he thinks his country must have good relations with all nations, whatever the regime or political orientation.

So now he is handing over to a team he has tested and trusts. This will not lead to spectacular changes. Most Cubans themselves - even those who criticise aspects of the regime - do not envisage or desire change: they don't want to lose the advantages it has brought them, the free education right through university, the free universal healthcare, or the very fact of a safe, peaceful existence in a country where life is calm.

While Castro turns full-time columnist, the main task for his political heirs will be how to confront the one perpetual challenge of Cuban life: relations with the US. We must wait to see if changes occur. Raul Castro has twice publicly announced he is prepared to sit down for talks with Washington on the problems between the two countries.

But it is in the US itself that a more appreciable political shift may come, with the Democratic frontrunner Barack Obama having signalled his willingness to engage with America's perceived enemies or adversaries, be it Iran, Venezuela or Cuba. An immediate and radical change may be unlikely, but there is reason to hope that November's election may at least alter the atmosphere after the Bush years - a presidency Castro regards as the most damaging to the whole planet of the 10 he has experienced.

The departure of Bush is likely to lead the US to a reappraisal of foreign policy: learning the disastrous lessons of Iraq and the Middle East, and returning the focus to Latin America. The US will find a changed situation: for the first time, Cuba has genuine friends in government in Latin America, most prominently Venezuela, but also in Brazil, Argentina, Nicaragua and Bolivia, a host of governments who are not particularly pro-American. It is in the US's interests to redefine its relations with all of them: non-colonial, non-exploitative and based on respect. Cuba, meanwhile, has developed closer relations with partner countries, as part of the EU-like ALBA economic and political organisation, and in agreements with the Mercosur trade area. In the bigger international picture, Cuba is no longer such a unique case.

It is on this international plane, developing ever stronger ties with Latin America, where the most visible changes in Cuban politics are likely to come. Its socialism will undoubtedly alter - but not in the manner of a China or Vietnam. Cuba will continue to go its own way. The new regime will initiate changes at the economic level, but there will be no Cuban perestroika - no opening up of politics, no multiparty elections. Its authorities are convinced that socialism is the right choice, but that it must be forever improved. And their preoccupation now, more than ever with the retirement of Castro, will be unity.

But everything in Cuba is related to the US: that is the one overarching aspect of political life which outsiders need to understand. The retirement of Castro, long anticipated, means continuity. But in the evolution of this small nation's history, the election of Obama could be seismic.

· Ignacio Ramonet is the co-author with Fidel Castro of Fidel Castro: My Life, and editor of Le Monde Diplomatique

comment@theguardian.com