On a long and reluctant journey to Damascus, as I researched the diaries and memoirs of the key figures involved, it dawned on me that my orthodox view of the cold war as a struggle to the death between Good (Britain and America) and Evil (the Soviet Union) was seriously mistaken. In fact, as history will almost certainly judge, it was one of the most unnecessary conflicts of all time, and certainly the most perilous.

The cold war began within months of the end of the second world war, when the Soviet Union was diagnosed as inherently aggressive. It was installing communist governments throughout central and eastern Europe. The triumphant Red Army was ready and able to conquer western Europe whenever it was unleashed by Stalin, who was dedicated to the global triumph of communism. But "we" - principally the US and Britain - had learnt from painful experience that it was futile to seek accommodation with "expansionist" dictators. We had to stand up to Stalin, in President Truman's phrase, "with an iron fist".

It was a Manichean doctrine, seductive in its simplicity. But the supposed military threat was wholly implausible. Had the Russians, devastated by the war, invaded the west, they would have had a desperate battle to reach the Channel coast. Britain would have been supplied with an endless stream of men and material from the US, making invasion virtually hopeless. And even if the Soviets, ignoring the A-bomb, had conquered Europe against all odds, they would have been left facing an implacable US: the ultimate unwinnable war. In short, there was no Soviet military danger. Stalin was not insane.

Nor was he a devout ideologue dedicated to world communism. He was committed, above all else, to retaining power, and ruling Russia by mass terror. Stalin had long been opposed to the idea that Russia should pursue world revolution. He had broken with Trotsky, and proclaimed the ideal of "socialism in one country". Foreign communist parties were encouraged to influence their own nations' actions. But it was never Stalin's idea that they should establish potentially rival communist governments. Yugoslavia and China were to demonstrate the peril of rival communist powers.

The cold war began because of Russia's reluctance to allow independence to Poland. Stalin was held to have reneged on promises at Yalta. Roosevelt and Churchill had demanded that Poland be allowed a government that would be "free" and also "friendly to Russia". It was a dishonest formula. As recently as 1920, the two countries had been at war. No freely elected Polish government would be friendly to the USSR. Furthermore, as Stalin pointed out at Yalta, Russia had been twice invaded through Poland by Germany in 26 years, with devastating consequences. The invasion of 1941 had led to the deaths of 20 million Russians. Any postwar Russian government - communist, tsarist or social democratic - would have insisted on effective control at least of Poland, if not of larger areas of eastern Europe, as a buffer zone against future attacks.

The cold war warrior Harry Truman came to office in April 1945. The existing White House, including the belligerent Admiral Leahy, convinced him that he must make an aggressive start. In May, Churchill told Anthony Eden, the foreign secretary, that the Americans ought not to withdraw to the lines previously agreed. There had, he said, to be a "showdown" while the Allies were still strong militarily. Otherwise there was "very little prospect" of preventing a third world war.

Churchill's iron curtain speech at Fulton, Missouri, in March 1946 - the phrase originated with Dr Goebbels, warning of the same red peril - reflects the great warrior's view of the Soviet menace. Not surprisingly, however, it was seen by the Russians as a threat. Referring to the new "tyrannies", Churchill said: "It is not our duty at this time when difficulties are so numerous to interfere forcibly in the internal affairs of countries." The inevitable implication was that there would be a time when difficulties were not so numerous.

Truman had adopted an aggressive attitude to Russia the previous October. He produced 12 points which he said would govern American policy, including the importance of opening up free markets. The programme would be based on "righteousness". There could be "no compromise with evil". Since half his points were aimed at Soviet rule in eastern Europe, the evil he had in mind was plain. He added that no one would be allowed to interfere with US policy in Latin America.

So Russian interference in countries essential to its safety was evil. But exclusive US domination of its own sphere of influence was righteous. In any case, a programme based on "no compromise with evil" is a preposterously naive basis for a foreign policy, destining a country to permanent warfare. (Perhaps, as the war against terrorism suggests, this is the capitalist world's version of Trotskyism.) The Atlantic Charter of 1941 was another example of humbug, with its declaration that countries should be free to elect their own governments. Churchill had later to explain that this did not apply to the British Empire. Molotov inquired what Britain intended to do about Spain. Spain was different, Churchill insisted.

Churchill's hostility to the Soviet Union was longstanding, despite the wartime alliance. He had proposed in 1918 that the defeated Germans should be rearmed for a grand alliance to march on Moscow. He supported the allied intervention in the Russian civil war. More important was his wartime theme that the Germans should not be disarmed too extensively because they might be needed against Russia. Moscow also suspected, with reason, that some British politicians had hoped appeasing Hitler would leave him free to attack Russia.

Against this background, it is unsurprising that the Soviet attitude was nervous and suspicious. The west made virtually no moves to allay these fears, but adopted a belligerent attitude to an imaginary military and political threat from an economically devastated and war-weary Russia. The fact that the cold war continued after Stalin's death does not, as some claim, prove the Soviets' unchanging global ambitions. The invasions of Hungary in 1956 and of Czechoslovakia in 1968 were brutal acts, but were aimed at protecting Moscow's buffer zone. The same may be said of the Soviet invasion of Afghanistan in 1980 (as a result of which, with the help of the CIA, the Taliban came into existence). In none of these cases was there a territorial threat to the west.

At times even Eisenhower seemed ambivalent about the cold war, warning about the vested interests of the American "military-industrial complex". Under his presidency US foreign policy had fallen into the hands of crazed crusaders such as John Foster Dulles. Followers of Dulles's crusading approach remained prominent, especially under Reagan, until the collapse of the Soviet Union.

Revisionist views of the cold war regularly surface in the US, though the case is sometimes spoiled by the authors' socialist sympathies (something of which I have never been accused). In Britain, the revisionist view has not had much of a hearing.

One can, of course, understand why few in the west want the orthodox view overturned. If that were to happen, the whole edifice of postwar politics would crumble. Could it be that the heavy burden of postwar rearmament was unnecessary, that the transatlantic alliance actually imperilled rather than saved us? Could it be that the world teetered on the verge of annihilation because post-war western leaders, particularly in Washington, lacked imagination, intelligence and understanding? The gloomy answer is yes.

· Andrew Alexander is a Daily Mail columnist, and is writing a book about the cold war. A longer version of this article appears in the current issue of the Spectator