America's two "great victories" since 11 September 2001 are unravelling. In Afghanistan, the regime of Hamid Karzai has virtually no authority and no money, and would collapse without American guns. Al-Qaeda has not been defeated, and the Taliban are re-emerging. Regardless of showcase improvements, the situation of women and children remains desperate. The token woman in Karzai's cabinet, the courageous physician Sima Samar, has been forced out of government and is now in constant fear of her life, with an armed guard outside her office door and another at her gate. Murder, rape and child abuse are committed with impunity by the private armies of America's "friends", the warlords whom Washington has bribed with millions of dollars, cash in hand, to give the pretence of stability.

"We are in a combat zone the moment we leave this base," an American colonel told me at Bagram airbase, near Kabul. "We are shot at every day, several times a day." When I said that surely he had come to liberate and protect the people, he belly-laughed.

American troops are rarely seen in Afghanistan's towns. They escort US officials at high speed in armoured vans with blackened windows and military vehicles, mounted with machine-guns, in front and behind. Even the vast Bagram base was considered too insecure for the defence secretary, Donald Rumsfeld, during his recent, fleeting visit. So nervous are the Americans that a few weeks ago they "accidentally" shot dead four government soldiers in the centre of Kabul, igniting the second major street protest against their presence in a week.

On the day I left Kabul, a car bomb exploded on the road to the airport, killing four German soldiers, members of the international security force Isaf. The Germans' bus was lifted into the air; human flesh lay on the roadside. When British soldiers arrived to "seal off" the area, they were watched by a silent crowd, squinting into the heat and dust, across a divide as wide as that which separated British troops from Afghans in the 19th century, and the French from Algerians and Americans from Vietnamese.

In Iraq, scene of the second "great victory", there are two open secrets. The first is that the "terrorists" now besieging the American occupation force represent an armed resistance that is almost certainly supported by the majority of Iraqis who, contrary to pre-war propaganda, opposed their enforced "liberation" (see Jonathan Steele's investigation, 19 March 2003, www.guardian.co.uk). The second secret is that there is emerging evidence of the true scale of the Anglo-American killing, pointing to the bloodbath Bush and Blair have always denied.

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Comparisons with Vietnam have been made so often over the years that I hesitate to draw another. However, the similarities are striking: for example, the return of expressions such as "sucked into a quagmire". This suggests, once again, that the Americans are victims, not invaders: the approved Hollywood version when a rapacious adventure goes wrong. Since Saddam Hussein's statue was toppled almost three months ago, more Americans have been killed than during the war. Ten have been killed and 25 wounded in classic guerrilla attacks on roadblocks and checkpoints which may number as many as a dozen a day.

The Americans call the guerrillas "Saddam loyalists" and "Ba'athist fighters", in the same way they used to dismiss the Vietnamese as "communists". Recently, in Falluja, in the Sunni heartland of Iraq, it was clearly not the presence of Ba'athists or Saddamists, but the brutal behaviour of the occupiers, who fired point-blank at a crowd, that inspired the resistance. The American tanks gunning down a family of shepherds is reminiscent of the gunning down of a shepherd, his family and sheep by "coalition" aircraft in a "no-fly zone" four years ago, whose aftermath I filmed and which evoked, for me, the murderous games American aircraft used to play in Vietnam, gunning down farmers in their fields, children on their buffaloes.

On 12 June, a large American force attacked a "terrorist base" north of Baghdad and left more than 100 dead, according to a US spokesman. The term "terrorist" is important, because it implies that the likes of al-Qaeda are attacking the liberators, and so the connection between Iraq and 11 September is made, which in pre-war propaganda was never made.

More than 400 prisoners were taken in this operation. The majority have reportedly joined thousands of Iraqis in a "holding facility" at Baghdad airport: a concentration camp along the lines of Bagram, from where people are shipped to Guantanamo Bay. In Afghanistan, the Americans pick up taxi drivers and send them into oblivion, via Bagram. Like Pinochet's boys in Chile, they are making their perceived enemies "disappear".

"Search and destroy", the scorched-earth tactic from Vietnam, is back. In the arid south-eastern plains of Afghanistan, the village of Niazi Qala no longer stands. American airborne troops swept down before dawn on 30 December 2001 and slaughtered, among others, a wedding party. Villagers said that women and children ran towards a dried pond, seeking protection from the gunfire, and were shot as they ran. After two hours, the aircraft and the attackers left. According to a United Nations investigation, 52 people were killed, including 25 children. "We identified it as a military target," says the Pentagon, echoing its initial response to the My Lai massacre 35 years ago.