Mazower tells us that Marx respected Randal Cremer, the British trade union leader, pacifist, and Liberal parliamentarian. (Also a Nobel peace laureate.) He does not tell us why Cremer quit the International Workingmen's Association. Marx and his crew, said Cremer, "cared more for their isms than for the cause of real progress". To hear Mazower tell it, the Soviet Union participated constructively in the Genoa Conference of 1922. He portrays the foreign affairs commissar, Georgy Chicherin, in an especially positive light. You would never know that Lenin's purpose in participating in the conference was to wreck it. He cabled Chicherin, "The fool Henderson & Co. will help us a lot if we cleverly prod them." "The fool Henderson" was Arthur Henderson, the British Labourite and fellow-traveller who would become foreign secretary and then a Nobel peace laureate.

Mazower is capable of the kind of generalising he would slam if it came from a conservative. For example, the Crimean War "revived the always latent belligerence of the British against the Russians". He speaks of racism against the Japanese, but never of Japan's own world champion racism. He condemns the colonialists in Africa, but has little to say about the butchers who succeeded them in power.

In the Cold War, you can be sure that America wears the black hat. The Truman Doctrine was an expression of "militarism". The Marshall Plan was basically a gambit, not an example of large-scale beneficence. Nixon, as a congressman, was just a "red-baiter", never mind that he was right about Hiss and Chambers. The likes of E.H. Carr were wise, but James Burnham wrote with "violence and crudity". (If Mazower had known Burnham, he would have found an erudition and scholarly excellence at least the equal of his own.)

The Green Revolution, like the Marshall Plan, was basically a Cold War gambit. Did men such as Norman Borlaug (another Nobel peace laureate) feed millions upon millions of starving? Forget that. Moving on to Vietnam, the Americans committed "war crimes" there. The Communists, during the war and after, committed no crimes, apparently. Reagan abetted human rights abuses in Latin America, rather than the democratisation of that region. He withdrew the US from Unesco, but why? Because the organisation was appallingly corrupt and needed to be pressured to reform? No, for bad reasons, evidently. Republicans in Congress withheld funds from the United Nations. To force reform? No, out of ignorant insularity.

In one of the oddest passages of his book, Mazower appears to blame America for the Srebrenica massacre and the Rwandan genocide. These events, he writes, "highlighted the limitations on UN power in the absence of strong American backing". I have heard the US blamed for a great many things; for those events, never, until now.

Mazower writes about "the dark days that followed the invasion of Iraq", but not about the dark days that preceded the invasion of Iraq ("rape rooms", children's prisons, chemical gassings, the cutting out of tongues for dissent). He lauds the International Panel on Climate Change — another Nobel laureate! — as though the scandals that rocked and discredited it had never occurred.

My catalogue could go on and on, but I will end it here, except to say this: a streak of meanness runs through this book. Mazower keeps sneering at liberal democrats who, whatever their mistakes, have done their best to help mankind. He sneers at the National Endowment for Democracy and Freedom House, for their funding by the US government. I dare say those groups do more good on an average day than Mazower or I do in a year.

Throughout the world, I have discovered, people are amazed that Americans don't have more respect for the United Nations. I often give them the example of the UN's human rights council — which has been graced by Gaddafi's Libya, Mugabe's Zimbabwe, the Communists' China, the Assads' Syria, the Castros' Cuba, genocidal Sudan, and other such beauties. Who can respect that? I also quote Solzhenitsyn — who said that the UN was not really the "united nations" but the united governments or regimes, only as good as the governments or regimes that compose it.

Having spent more than 400 pages with Professor Mazower, I feel sure he would call me a "red-baiter". But readers can judge for themselves the character of his remarkable book. Reading him is like being lectured by the best left-wing professor you'll ever have. Or like reading the best foreign affairs writer the Guardian or the Nation has to offer. (Those are two publications for which Mazower writes.) You can learn a lot from him, but you have to put up with a lot.