The first Democratic president in the modern era to be elected on an anti-war ticket is also, to the relief of neocons and the liberal belligerati, a hawk. Committed to escalation in Afghanistan, his foreign policy selections also indicate bellicosity towards Sudan and Iran. During his first week in office he sanctioned two missile attacks in Pakistan, killing 22 people, including women and children. And his stance on Gaza is remarkably close to that of the outgoing administration. The question now is how Obama will convince his supporters to back that stance. Bush could rely on a core constituency whose commitment to peace and human rights is, at the very least, questionable. Obama has no such luxury. In making his case, he will need the support of those "liberal hawks" who gave Bush such vocal support.

It is tempting to dismiss the "pro-war left" as a congeries of discredited left-wing apostates and Nato liberals. Their artless euphemisms for bloody conquest seem especially redundant in light of over a million Iraqi deaths. Yet their arguments, ranging from a paternalistic defence of "humanitarian intervention" to the championing of "western values", have their origins in a tradition of liberal imperialism whose durability advises against hasty dismissal. In every country whose rulers have opted for empire, there has developed among the intellectual classes a powerful pro-imperial consensus, with liberals and leftwingers its most vociferous defenders.

Liberal imperialists have resisted explicitly racist arguments for domination, instead justifying empire as a humane venture delivering progress. Even so, implicit in such a stance was the belief that other peoples were inferior. Just as John Stuart Mill contended that despotism was a "legitimate mode of government in dealing with the barbarians" provided "the end be their improvement", so the Fabians contended that self-government for "native races" was "as useless to them as a dynamo to a Caribbean". Intellectuals of the Second International such as Eduard Bernstein regarded the colonised as incapable of self-government. For many liberals and socialists of this era, the only disagreement was over whether the natives could attain the disciplined state necessary to run their own affairs. Indigenous resistance, moreover, was interpreted as "native fanaticism", to be overcome with European tuition.

The current liberal imperialists are not replicas of their 19th-century antecedents. Cold war priorities, including the need to incorporate elements of the left into an anti-communist front, transformed the culture of empire. If the "anti-totalitarian" left supported US expansionism, they often did so under the mantle of anti-colonialism. Decolonisation and the civil rights struggle meant explicit racism had to be dispensed with in arguments for military intervention.

This was a slow process. Both the Eisenhower and Kennedy administrations were terrified of "premature independence" for colonised nations. The state department asserted that "backward societies" required authoritarianism to prepare them for modernity. Irving Kristol, a cold war liberal who became the "godfather of neoconservatism", justified the Vietnam war in part by asserting that the country was "barely capable of decent self-government under the very best of conditions", and thus needed its US-imposed dictatorship. Nonetheless, such arguments today tend to be rehearsed only on the wilder shores of the neoconservative right.

Since the collapse of the Soviet Union, however, some paternalistic mainstays of liberal imperialism have been reinvented under the impress of "humanitarian intervention". Just as Victorian humanitarians saw the empire as the appropriate tool for saving the oppressed, so the 1990s saw demands for the US military to deliver Somalians, Bosnians and Kosovans from their tormentors - notwithstanding the fact that US intervention played a destructive role in each case.

The agency of the oppressed themselves is largely absent from this perspective. And, as New York University's Stephen Holmes pointed out: "By denouncing the United States primarily for standing by when atrocity abroad occurs, these well-meaning liberals have helped re-popularise the idea of America as a potentially benign imperial power."

The catastrophe in Iraq has produced a reaction against humanitarian imperialism even from former interventionists like David Rieff, who has warned against the "rebirth of imperialism with human rights as its moral warrant". Even so, among liberal intellectuals there is a broad coalition favouring intervention into Darfur, though humanitarian organisations have opposed the idea. And there is little resistance to the escalation in Afghanistan, where "native fanaticism" is once more the enemy. Liberal imperialism is in rude health: it is its victims who are in mortal peril.

• Richard Seymour is the author of The Liberal Defence of Murder leninstombblog@googlemail.com