Many years after Ernesto "Che" Guevara's death in 1967, Fidel Castro confessed: "I dream of Che a lot. I dream he is alive ... that we talk." The pair met in Mexico City in 1955 and together they masterminded the Cuban revolution, forging a tight friendship which, Simon Reid-Henry argues, was as important as that of Marx and Engels. This well-researched biography, the first in-depth exploration of that friendship, is an absorbing read despite needing more colour and additional editing. Reid-Henry skilfully conveys the contrasting personalities of the two revolutionaries and illustrates the immense influence Che's idealism had on the political strategist Castro, even from beyond the grave.

The subject of Simon Reid-Henry's book is a friendship that came to symbolise the Cuban revolution of 50 years ago: two men united in purpose, whose primary adult relationship was with each other, though not physically so, since machismo has a horror of homosexuality. Both were privileged, spoilt in childhood and overflowing with self-belief. Each was sexually predatory, with serial relationships and many children. For both, the political mission was what counted and each had a sense of destiny that was, at best, a mixed blessing in power.

When Fidel and Che met, in Mexico in 1956, Fidel was a revolutionary in exile, the Jesuit-educated bastard son of a landowner from Cuba's Oriente province. He had one military debacle to his name (the assault on the Moncada barracks in 1953) and another in the planning stages (the Granma landing). Both disasters proved useful in the serious work of constructing a revolutionary myth that starred Fidel.

Ernesto Che Guevara was the privileged son of a wealthy Argentine family, a self-declared communist in search of a meaning to life. For him, it seems to have been love at first sight. He threw in his lot with Fidel, sailed with him on the Granma and evolved into a skilful guerrilla leader in the Sierra Maestra, becoming one of the central figures in the revolution that triumphed with the flight of Batista in 1959. In the snakepit of Cuban politics, the two men maintained a level of mutual trust, in part by conspiring against others.

What each really believed at any given moment is hard to judge. The revolution began as a broad movement of liberals, social democrats, communists, nationalists and opportunists against a crumbling dictatorship that even the US, by then, declined actively to support. Its retroactive redefinition as socialist by Fidel served other needs, among them Fidel's consolidation and monopoly of power. On both a personal and an intellectual level, Reid-Henry argues, Che served as an ideological vanguard for Fidel's more manipulative political operation.

The question of why Che left Cuba in 1965 to resume his career as a revolutionary fighter, first in Congo and then in Bolivia, remains as open to speculation as before. Some argue that Fidel wanted to get rid of a potential rival and obstacle to his own shifting foreign relations; others - and Reid-Henry inclines to this camp - that they shared the dream of replicating the Cuban revolution around the world. If true, it argues an extraordinary naivety on the part of the two revolutionaries, coupled with a fatal tendency to believe in their own mythology.

For readers new to the subject, Reid-Henry offers a readable synthesis of the dramatic events of half a century ago, but it is a pity that he did not take his analysis of this key relationship a little further. After Che's death in Bolivia, Fidel embraced first the USSR, then China, while Che's posthumous career as international icon flourished. Tourists to Cuba come home with Che-themed T-shirts and ashtrays, and feature films re-mythologise his story for new generations.

Today, Fidel is a sick old man who has presided over decades of stagnation in Cuba. The ghost of Che is honoured everywhere - the ageless revolutionary and embodiment of high moral principle and self-sacrifice, unwithered by the passage of time or the less-than-heroic reality. The partnership continues.

 Isabel Hilton is the editor of chinadialogue.net

Simon Schama is many things: widely ranging historian, art critic, public intellectual, television don. For some, he's a bit too flashy, with a prose style glittering (at times) with fake jewels. On the other hand, a wide audience finds in him a rare form of intellectual entertainment, at once provocative and informative. As usual, in his latest multimedia production he swerves from past to present with staggering dexterity. The television series is already under way, so how does it do as a book?

Few writers can summon an era so well, or so briskly, with a telling anecdote or well-phrased aside. His unwieldy subject here is the US itself, where he has spent a good deal of his adult life, and which he understands deeply. Yet this book remains elusive. In many ways, it's a sequence of riffs on American history accompanied by heady intimations of where things are going, and where they might go.

He opens with jaw-dropping audacity, saying he knows exactly when American democracy came back from the dead: on January 3 2008, during the Iowa caucus. He was there, he tells us: almost a spoof on the eyewitness account. We know what he means: that the rise of Barack Obama has had something to do with a resurgence of grassroots democracy. But he might as well have chosen any number of other anticipatory moments, such as the unlikely emergence of Howard Dean in 2004.

Schama likes a good story. History, for him, is narrative, although he insists that we should "retire the word 'narrative' - from graduate student courses; political analysts; image doctors; from anyone who doesn't actually narrate". Despite this remark, Schama narrates with gusto. And his narratives are not just one damn thing after another (to quote Arnold Toynbee); instead, he makes elaborate links, finding the plots in history, its hidden and necessary connections.

An enthusiast for Obama, Schama turns his hero into a narrative historian, something like himself: "When Obama spoke of wanting to replace the partisan division of 'Red States' and 'Blue States' with a recovered United States, it was impossible not to remember Thomas Jefferson's inaugural, after the bitter election of 1800 that (after 39 ballots of the House of Representatives) finally brought him to power." This is, perhaps, the proper role of the historian: to bring past and present together, using the one to illuminate the other.

Surprises abound in Schama's work. I recall a passage in Landscape and Memory (1995), perhaps his finest book, where he summons a vision of the pristine "brilliant meadow floor" of Yosemite. It seemed a kind of Eden to the European eyes that first encountered it, God's dream of paradise; yet it was the product of systematic fire-clearances by the Ahwahneechee Indians who lived there long ago. What you think you see is often not what you get.

This larger truth applies nicely to American history. For instance, Schama opens one section with a quotation from Dick Cheney: "America has never been a warrior culture." Like hell we haven't. Schama makes his point by following one American family, the Meigs, who appear always to have had someone on the field of battle. We hear about one Montgomery Meigs, who had worked with young Robert E Lee in the summer of 1837 on the Mississippi, surveying the river. When Lee eventually took up arms against the union, Meigs took it personally. His descendent, General Monty Meigs, appeared at the White House in 2006 to brief Dick Cheney, George W Bush and Donald Rumsfeld about the dire situation on the ground in Iraq. This is history by example, channelling large abstractions into particular illustrations.

Schama revels in ironies, as in his shrewd meditations on immigration, where he points out that the US, while a nation of immigrants, has always taken a dim view of those currently aspiring to citizenship. There has been a persistent fear of losing one's identity in the melting pot. Schama, the son of Jewish refugees, has a gut understanding of what it means to feel displaced, and how difficult assimilation can be.

In a section called "American Fervour", he contemplates the curious passion that has underscored the American experience for generations, taking many forms - religious or political. There is always that search for the Promised Land, a place where all will be well. "The American future is all vision," Schama writes, "numinous, unformed, light-headed with anticipation". As ever, he revels in the contrast between this visionary gleam and the dark past that weighs it down.

This ragged, brilliant, hopscotching volume of vaguely connected essays is largely about America's myth of its own exceptionalism, the belief that somehow the American will must triumph in the world. The appeal as well as the ruthlessness of this vision comes through in these pages. I was left feeling rather chilled by Schama's take on the US and its prospects. This may be the end of an empire as we knew it, and one can only wonder what it will mean for someone like Obama to preside over its dismantling - or its transformation.

 Jay Parini's forthcoming book is Promised Land: Thirteen Books That Changed America (Doubleday)