Patrick Cockburn: The battle to justify this as a war worth fighting just got a lot harder

Pictures of prisoners being tormented in Abu Ghraib led to a tidal wave of revulsion against the US occupation of Iraq. The release of the vast archive of US military documents on Afghanistan is not likely to have the same explosive impact, but the sheer nastiness of the conflict is vividly conjured by the cumulative effect of thousands of uncensored reports from the frontline. The "Afghan Files" explain why the Kabul government is getting weaker, despite the fact that the US now has over 90,000 troops fighting 28,000 Taliban at a cost of $300bn (£190bn) over the last nine years.

And they will make it still harder in future for the US and British governments to explain why they are fighting to preserve an Afghan government so rotten with corruption and brutally uncaring towards its own people.

Much of what is now documented from official sources had already been exposed by journalists. But the 91,000 leaked reports paint a more detailed picture than ever before of the realities of life in contemporary Afghanistan.

As with Abu Ghraib, the reality of the Afghan war as described by frontline US officers and officials is as bad or worse than anything reported by the media.

As was to be expected, the White House and the Pentagon have denounced the revelations as giving aid and comfort to the enemy. Yet few secrets have actually been revealed.

Afghans know all too well that US-led death squads have long been arbitrarily killing suspected Taliban, along with anybody else who got in their way.

The fact that more Afghan civilians were being gunned down at checkpoints or killed by ill-directed air strikes than was officially admitted will come as no surprise to Afghans who have been at the receiving end of coalition firepower.

It has been difficult hitherto to convey what words like "brutality" and "corruption" mean in their Afghan context. But some of the incidents now go a long way to explaining why so many ordinary Afghans are driven into the hands of the Taliban.

For instance, in Balkh province in northern Afghanistan, a report was made on 11 October 2009 about soldiers and police mistreating local people who refused to cooperate in a search. A district police chief raped a 16-year-old girl and when a civilian protested, the police chief ordered his bodyguard to shoot him. The bodyguard refused and was himself killed by the police chief.

Corruption is so pervasive that a substantial part of the income of poor villagers is spent bribing officials. A recent opinion poll showed that Afghans regard endemic corruption as a greater threat even than insecurity. Anybody can be targeted. One US investigator had seven policemen in the south-eastern province of Paktia arrested for extorting money from motorists passing through their checkpoint.

The policemen explained that they had to do so to buy fuel for their generator if they wanted to have any electricity.

The presence of foreign forces and their vulnerable supply lines opens the door to profitable protection rackets. In one instance, a fuel convoy travelling from Kandahar to Oruzgan was stopped by 100 well-armed insurgents who demanded $2,000 a truck to let it proceed. The insurgents turned out to work for Matiullah Khan, a pro-government, US-backed warlord in Oruzgan who was already being paid by the Afghan Interior Ministry to protect Nato convoys on the road.

One value of many of these ground-level reports is that they have not been edited or censored by senior officials. They are honest about what Afghans really think of the US-led coalition.

The Taliban began their comeback in 2006 and by 2007 it was in full swing. In September that year, in the town of Gardez, provincial council officials spoke frankly to an American civil affairs official about the way they thought things were going. "The people of Afghanistan keep losing their trust in the government because of the high amount of corrupt government officials," one said. "The general view of the Afghans is that the current government is worse than the Taliban."

The US official recorded bleakly: "The people will support the Anti-Coalition forces and the security condition will degenerate."

How accurate are the reports? Those by US officials reflect their perception of what was happening while those by Afghans about Pakistani involvement in support of the Taliban are dubious.

It is certainly true that, overall, Pakistani military intelligence does have a strong influence, but not quite full control, over the Taliban.

The Taliban safe havens in Pakistan are never quite safe and the Taliban say privately that while they can generally operate in Pakistan, they never know when they might be arrested.

Overall, the Wikileaks dossier gives the impression of the US military machine floundering into war and only gradually realising the crippling weakness of the Afghan government. There is intermittent understanding on the ground that the presence of foreign occupation forces is itself the main recruiting sergeant of the Taliban.

Above all, the documents convey a sense of bewilderment that the US military should be making such great efforts and achieving so little.