These four volumes, like Diderot's Encyclopédie, are not just a mine of information but a work of propaganda. As the Dalai Lama says in his high-minded introduction, they are a peace project as well as an academic project. Their mission is to provide knowledge that will improve humanity. They aim to help transform the military-industrial culture of the modern world into something more wholesome, to promote cooperation instead of conflict and to establish a reign not simply of peace but of justice. In the words of the chief editor, Nigel J Young, the ethical impetus behind The Oxford International Encyclopedia of Peace is "the humanitarian morality" of the French philosophes.

This does not mean that he has allowed his contributors  more than 500 scholars from all over the world  to wax too polemical. But they were permitted to express their own views and he hopes that a balance has been achieved by "the juxtaposition of multiple perspectives". There is certainly a variety of opinions in the 850 articles, which proceed alphabetically from "Abraham Path Initiative" to "Zones of Peace". The content is supported by useful (though not comprehensive) bibliographies. Also included is a chronology of "peace in history" (listing treaties, publications and so on), a glossary of technical terms and a selection of key documents. Among them is the Encyclopédie's article on peace, which declares that "War is the fruit of man's depravity."

This is the central message of the Encyclopedia of Peace. Concentrating mainly on the contemporary scene, it provides a cornucopia of pertinent facts and liberal ideas about its bloody state. There are telling statistics: in the first world war 10% of the casualties were civilians; in the second world war the figure was 45%; in conflicts during the 1990s the civilian toll reached 90%, including 2 million children killed and 6 million maimed. There are revealing details: in December 2006 America was the only country in the UN to vote against a treaty to prevent human rights abuses by setting uniform standards for arms deals. There are fascinating insights: one article demonstrates the interdependence of war and genocide.

There are cogent arguments: Paul Oestreicher makes a good case for saying that state terrorism (as practised, say, by Israel) should be outlawed. There are piquant quotations, such as Gorbachev's remark to Mrs Thatcher: "We are going to do something horrible to you  we are going to deprive you of an enemy." There is also an impressive consensus about the futility of George Bush's "war on terror". Like the 1953 Anglo-American coup against Mossadeq in Iran, the illegal invasion of Iraq has produced a horrid series of unintended consequences. Among them is the spread of suicide bombings, even to Afghanistan, where 118 occurred in 2006  more than in the entire previous history of the country. One article aptly cites Steve Bell's spoof recruitment poster: "British Army's New Afghan Die As You Learn Scheme."

Sad to say, however, the merits of the Encyclopedia of Peace are counter-balanced by grave shortcomings. The sine qua non of such a compilation is that it should be accurate, and it is not. Young misspells Eric Hobsbawm's name in the introduction and this is merely the first of many similar slips. In a single parenthesis in Geoffrey Robertson's otherwise admirable article on human rights, for example, both JB Priestley and Barbara Wootton are spelt wrongly. Other errors abound: the battle of Solferino took place in 1859, not "during the Napoleonic wars"; when Michael Foot co-wrote Guilty Men he was a journalist not "a Labour party leader"; Japan invaded Manchuria in 1931 not 1932; Hemingway's novel A Farewell to Arms was set in the first world war not the second.

More fundamentally, there are mistakes of interpretation. An article on appeasement, for instance, states that this pacific policy was defunct after 1945 and that "no statesman would dare to propose it". Churchill himself is cited to back up this view since, in the first volume of his war memoirs, published in 1948, he criticised Chamberlain for appeasing Hitler. What the article entirely ignores (and what many have ignored since) is Churchill's qualification as he prepared to seek détente with the Soviet Union. "Appeasement in itself may be good or bad according to the circumstances," he told parliament in December 1950. "Appeasement from strength is magnanimous and noble and might be the surest and perhaps the only path to world peace."

As this suggests, the quality of the articles is exceedingly uneven. Some are excellent but more are banal, tendentious and repetitious. Not a few are so full of sociological jargon as to be virtually unintelligible. Thus: "In contrast to psychological, economic, or political monocausalism, Bouthoul's polemological theory is polycausal." There is also the problem, ruefully acknowledged by several contributors, that war, though ghastly, is full of thrilling particulars whereas peace, though desirable, is boring and nebulous.

Significantly Diderot called his Encyclopédie a machine de guerre. It was the Enlightenment's ideological weapon against the ancien regime. Even its definitions conspired to undermine the established order: "One is bound to one's wife but attached to one's mistress." But where Diderot was subversive, Young's Encyclopedia is platitudinous, advocating peace as Americans advocate motherhood and apple pie. Perhaps, like Wikipedia, it should have been published electronically so that its more glaring deficiencies could be corrected at the touch of a button.

Piers Brendon's The Decline and Fall of the British Empire is published by Vintage.