"To be able," wrote the late Christopher Hitchens, "to bray that 'as a liberal, I say bomb the shit out of them,' is to have achieved that eye-catching, versatile marketability that is so beloved of editors and talk-show hosts. As a life-long socialist, I say don't let's bomb the shit out of them. See what I mean? It lacks the sex appeal, somehow. Predictable as hell." That was in 1985.

In 2002, he took a different view of the matter. As long as the bombs were hitting the bad guys, then "it's pretty good because those steel pellets will go straight through somebody and out the other side and through somebody else … They'll be dead, in other words."

Predictable as hell or not, this transfiguration placed Hitchens (pictured in 1978) in a recognisable category: the left-wing defector with a soft-spot for empire. The episodes in Hitchens's shift to the right are well-known: the Rushdie affair, the Bosnia wars, the skirmishes with the Clinton White House and finally 9/11. The main conclusions that Hitchens drew from these were that religion, and specifically Islam, was an underestimated force for evil in world affairs, that the US empire could be a countervailing force for good, and that the left had become detached from any international working-class movement capable of challenging capitalism, and was on the wrong side of history.

This combination of views was not cut, wholesale, out of new cloth. Rather, components of his long-standing beliefs took up enlarged roles in a new world view. His fascination with America, his "anti-theism", and his faith in war as a positive force (for example, his support for Britain during the Falklands war) had long been elements in his thinking. Similarly, his enthrallment with the right, as the truly "revolutionary", dynamic force, can be detected in some of his writings about Thatcherism, and indeed about Thatcher herself ("pure sex").

Hitchens denied that his changed views after 2001 placed him on the right. His sycophants and sympathisers likewise find the idea hard to take. They point to his humanist atheism, his baiting of old bigots such as Pat Robertson and Jerry Falwell, and his occasional criticisms of the Bush administration. They also cite the perishing embers of leftist sympathy evident in some of his literary writing.

But while it's certainly true that Hitchens reviled the religious right, his views were in most respects remarkably close to those of the neocons. This is most visible in his support for the invasion of Iraq. Hitchens justified his support for war on a number of grounds, but the keynotes were humanitarian and liberal. The Ba'ath regime was rebarbative, while the US was a pluralist society – Iraq could become the same. More broadly, America had found itself "at war with the forces of reaction" since September 2001. He was for "revolution from above", he claimed, a concept that is telling.

Hitchens was, not for the first time, drawing on the conceptual repertoire of his quondam Trotskyism to justify his stance. In the critical idiom of Marxism in which he was educated, a "revolution from above" could mean many things. But one connotation, as he knew, was the establishment by force of "people's democracies" in Eastern Europe after the second world war – in other words, Stalinist imperialism. His own use of the term, as he explained, referred to "what colonial idealists used to call the 'civilising mission'". In the run-up to the invasion, Hitchens joined the Committee for the Liberation of Iraq, demanding the final extension and conclusion of the first Gulf war's "Desert Storm" (a war which he had always argued was imperialist) along neocon lines. He extolled a "new imperialism", whose sole remit was to enable local populations to govern themselves. In fact, there was absolutely nothing new about imperialism being justified in such terms. Still, "if the United States will declare out loud for empire, it had better be in its capacity as a Thomas Paine arsenal, or at the very least a Jeffersonian one".

The moral rearmament of imperialism along these lines was a hallmark of neoconservatism. It was the neocons who pioneered the hypocritical "human rights" discourse that justified Reaganite revanchism in the 1980s, they who pioneered the practice of appropriating the language of leftist internationalism for reactionary purposes.

If Hitchens refused the label of conservative, it was largely because of his peculiar understanding of historical progress. It was important for him to be on the "right side" of history, on the side of those forces which had the greatest dynamism and potential power. During his time as a leftist, there were moments when this sympathy for the powerful in history showed. He always felt, for example, that the British Empire had a progressive role in India. He wrote of Columbus Day that the extermination of the Native Americans should be celebrated as a fact of historical progress. By the end of his life, Hitchens was convinced that American capitalism was "the only revolution in town", and that it would be "a step up" for the countries exposed to it by armed occupation.

The worst of all this, perhaps, is that Hitchens might have seen what was coming. He spent much of his life as a writer skewering apostate leftists who ended up as red-faced rotarians or belligerent bombers – from Paul Johnson to Conor Cruise O'Brien. His tragedy, which his careful revisions and rationalisations cannot conceal, is that he became what he had despised – as Hazlitt put it, "a living and ignominious satire upon himself".

• Richard Seymour's Unhitched: The Trial of Christopher Hitchens is due from Verso.