Official America's reaction to the largest leak of confidential government files in history is tipping over towards derangement. What the White House initially denounced as a life-threatening "criminal" act and Hillary Clinton branded an "attack on the international community" has been taken a menacing stage further by the newly emboldened Republican right.

WikiLeaks' release of 250,000 United States embassy cables – shared with the Guardian and other international newspapers – was an act of terrorism, congressman Peter King declared. Sarah Palin called for its founder Julian Assange to be hunted down as an "anti-American operative with blood on his hands", while former presidential candidate Mike Huckabee has demanded that whoever leaked the files should be executed for treason.

Not much truck with freedom of information, then, in the land of the free. In reality, most of the leaked material is fairly low-level diplomatic gossip, which naturally reflects the US government's view of the world, and crucially doesn't include reports with the highest security classification.

When it comes to actual criminality and blood, nothing quite matches WikiLeaks' earlier revelations about the wars in Iraq and Afghanistan, with their chilling records of US collusion with industrial-scale torture and death squads, and killings of Afghan civilians by rampaging Nato troops.

Nor, of course, is what US diplomats write necessarily true. But beyond the dispatches on Prince Andrew's crass follies and Colonel Gaddafi's "weirdness", the leaks do paint a revealing picture of an overstretched imperial system at work, as its emissaries struggle to keep satraps in line and enemies at bay.

Much has been made of the appalling damage supposedly done to the delicate business of diplomacy. No doubt the back channels will survive the shock of daylight. But in any case the United States is the centre of a global empire, a state with a military presence in most countries which arrogates to itself the role of world leader and policeman.

When genuine checks on how it exercises that entirely undemocratic power are so weak at home, let alone in the rest of the world it still dominates, it's both inevitable and right that people everywhere will try to find ways to challenge and hold it to account.

After the Russian revolution, the secret tsarist treaties with Britain and France were published to expose and challenge the colonial carve-ups of the day. In the 1970s, the publication of the Pentagon papers cut the ground from beneath the US case for the Vietnam war. Now technology is allowing such exposures on a far grander scale.

Clinton complained this week that the leaks "tore at the fabric" of government and good relations between states. Far more damaging is her own instruction to ordinary US diplomats to violate the treaties the US government has itself signed and spy on UN officials, along with any other public figure they happen to meet: down to their credit card details, biometric records – and even frequent-flyer account numbers.

Not surprisingly, US allies and client states come out badly from the leaks. The British government is once again shown to kowtow to US demands for no gain, first promising to "put measures in place" to protect American interests in the Iraq war inquiry, and then colluding in a plan to deceive parliament and allow the US to keep banned cluster-bombs in its bases on Diego Garcia (in exchange for which Gordon Brown was firmly rebuffed by the US over the extradition of the British computer hacker Gary McKinnon).

But it is the relentless US mobilisation against Iran that provides the most ominous thread in the leaked despatches. The reports that the king of Saudi Arabia has called on the US to "cut off the head of the snake" and launch what would be a catastrophic attack on Tehran, echoed by his fellow potentates in Jordan, Egypt, the United Arab Emirates, Bahrain – and, of course, most dangerously by Israel – were yesterday hailed by the Times as evidence of a new "international consensus" against Iran.

It is nothing of the sort. It simply underlines the fact that after more than half a century the US still has to rely on laughably unrepresentative autocracies and dictatorships to shore up its domination of the Middle East and its resources. While Arab emirs and election-rigging presidents fear the influence of Iran and only wearily bring themselves to raise the Palestinians with their imperial sponsors, their people regard Israel and the US itself as the threats to their security and strongly support Iran's nuclear programme – as the most recent US-conducted poll in the region demonstrated.

The confirmation in the cables that US military forces are indeed secretly operating on Pakistan's territory and that Yemen's president Abdullah Saleh felt it necessary to tell General Petraeus this year that he would carry on lying about US military operations against jihadists in his country – "we'll continue saying they are our bombs, not yours" – only emphasises how weak and illegitimate US props and allies are across the Muslim world.

But it's those who have helped to expose such lethal campaigns who are now charged with "putting lives at risk". Assange is threatened with ever more dire retribution and Bradley Manning, the 23-year-old US army intelligence analyst accused of leaking the Iraq, Afghanistan and diplomatic cables is already facing up to 52 years in prison. Meanwhile the aircrews of two US Apache helicopters who killed a dozen unarmed civilians in Iraq in 2007 as they laughed and crowed – the video of which Manning is alleged to have leaked – were commended by US central command for their "sound judgment".

Manning is reported to have said that the latest leaks show how "the first world exploits the third". But they also cast a powerful light on how the US empire has begun to flounder as the post-cold war unipolar moment has passed, former dependable client states like Turkey go their own way and independent regional powers such as China start to make their global presence felt.

By making available Washington's own account of its international dealings WikiLeaks has opened some of the institutions of global power to scrutiny and performed a democratic service in the process. Its next target is said to be the leviathan of the banks – bring it on.

• This article was amended on 2 December 2010. The original referred to Peter King as a senator. This has now been corrected