So why did the first world war begin in August 1914, and how should it be remembered?

Ignore the complexity of the different situations, interests and alliances of the various European governments who shared responsibility for the conflict.

In brief, Britain and France had colonial empires and sought to retain them, while imperial Germany's interest was to expand its little empire, which was much smaller than France's, which was in turn much smaller than Britain's.

Kaiser Wilhelm's Germany had long-term aims to extend influence eastwards, as well as to obtain African colonies.

France, to protect its position against Germany, had formally engaged as long ago as 1891 - after losing Alsace and Lorraine to Germany in 1870 - to support reactionary and semi-feudal, "holy" tsarist Russia if that country were attacked.

Imperial Austria-Hungary had annexed mainly Serb-populated Bosnia in 1908. It was now plagued by repeated terrorist incidents at the hands of nationalist Serbs.

Serbia, if attacked by Austria, could rely on Russia to come to its aid. But if Russia did so, and was itself threatened, it could bank on France's military support.

On the other hand, Austria could call on Germany's support if threatened by Russia. Britain, meanwhile, was bound by secret obligations to commit its forces in France's support if France were menaced.

As far back as 1889 Karl Marx's collaborator and friend Friedrich Engels, emphasising the importance for the socialist movement of the fight to maintain peace, had expressed in a letter his fear of a future European war "in which there will be 10 to 15 million combatants, an unheard of devastation, universal violent suppression of our movement, the recrudescence of chauvinism in every country."

In this tense international environment the crisis which could produce war on a European scale could spring up anywhere, but the "Austria-Serbia dispute" was the likely point of combustion and had been so identified in the manifesto of the Basle Socialist International Conference in 1912.

It was there, wrote AL Morton in his unrivalled A People's History of England, "that the greatest possibilities of diplomatic aggravation existed."

Sarajevo, the Bosnian capital, was on June 27 1914 the scene of the last and deadliest of a series of terrorist outrages on Bosnia's Austrian rulers by a group of Serbian nationalists.

Within hours of a botched bomb attack on the emperor's nephew Archduke Ferdinand advantage was taken of a chance opportunity to complete the job and Ferdinand and his wife were shot dead at close range.

Over the next two weeks in British Labour circles consciousness of war danger grew. Labour Party chairman WC Anderson wrote in the Labour Leader on July 9: "Official statements issued raise the suspicion that Austria-Hungary looks upon the present as a favourable opportunity for picking a quarrel with her Serbian neighbour. This is a dangerous game, for, the moment the peace is broken, various Big Powers will be drawn in."

Before the end of July Austria declared war on Serbia. Russian mobilisation followed.

On August 1 Germany declared war on Russia and the next day issued an ultimatum requiring free passage through Belgium for German troops.

On August 3 Germany declared war on France and crossed into Belgium en route for France. On August 4 Britain declared war on Germany. Austria's declaration of war on Russia followed on the 6th. Britain and France's respective declarations of war on Austria a few days later completed the formalities authorising mutual massacre.

"So," to quote Morton again, "the train ran from point to point, till the European powder magazine, so zealously crammed with explosives by the labour of a generation, went up in one vast roar."

Extraordinarily foreign minister Sir Edward Grey appeared to have no perception of what lay ahead when he addressed the House of Commons on August 3. "If we are engaged in war," he said, "we shall suffer but little more than we shall suffer if we stand aside."

Germany's non-compliance the next day with Britain's ultimatum to respect Belgian neutrality equalled war.

It raged remorselessly for the next four years. Millions of lives were shattered because, wrote the radical Liberal ED Morel in Truth and the War, "one of the great ones of the Earth had fallen beneath the hand of the assassins in a far distant country, because the other great ones had quarrelled as a result of that crime, because the rulers of Christian Europe had for years been squandering the substance of their peoples in piling up weapons destructive of human life until all Europe was one great arsenal, and had planned and schemed against each other through their appointed agents..." Responsibility, wrote Morel, was "distributed."

Had the German fleet, already mobilised, first attacked France or French shipping, and had the British fleet then engaged German warships as Britain had promised secretly to do through military staff conversations, and promised again to do on August 2, Britain's government would not have been able to window-dress the case for war as one for upholding an obsolete treaty to protect Belgium.

Had Foreign Office records then been available for public inspection, they would have revealed too that if France sent its own troops through Belgium en route to Germany, Belgium would be left to fend for itself.

As it was, Britain was extravagantly to claim it was fighting a war for civilisation.

So what had the anti-war movement done, across Europe, to stop the continent's transformation into a graveyard?

In Britain, repeated wake-up calls from anti-war socialists such as Keir Hardie, George Lansbury and John Maclean had reached back across the years.

In mid-April 1914 the Independent Labour Party's annual conference at Bradford was an occasion for more of the same. "This conference protests," the Labour Leader reported, "against the ever-increasing burden of armaments and preparations for war, welcomes the growing international solidarity of the workers as a potent force for peace."

On the last day of April 1914 an article by Hardie in the same paper focused on the risk of war. "War cannot be made without the consent of the common people. True, their consent is not asked, but if the rulers know that the workers will not fight each other no war will ever be declared. That much is obvious, and a consideration of that fact is an additional argument for the anti-war strike propaganda of the International Socialist Bureau."

An emergency meeting of the bureau at Brussels almost at the end of July was attended by Hardie and Germany's Rosa Luxemburg, whose anti-conscription position had already earned her a prison sentence, so far deferred by an appeal process.

This meeting produced a call for increased pressure on governments to maintain peace. But when war began, the majority leaderships of the chief labour parties rallied to their respective governments.

Luxemburg and William Liebknecht led a minority of anti-war German socialists, while Russia's Bolshevik Party led by Lenin maintained a firmly anti-war position. In France, on the last day of July, the anti-war socialist leader Jaures was assassinated.

On August 2 1914 the largest of many anti-war rallies around Britain took place in Trafalgar Square. Four days later, with war now official, the Labour Leader shouted: "Down with the War!", declaring to its readers: "You have no quarrel with Germany. The quarrel is between the ruling classes of Europe."

Hardie wrote: "The angel of death with bloodstained wings is hovering over Europe."

Hardie was howled down by war supporters when speaking at Aberdare, while John Maclean was to face the question "Why don't you enlist?" when addressing a Glasgow audience.

He answered: "I have been enlisted for 15 years in the socialist army, which is the only army worth fighting for. God damn all other armies." For such remarks he was soon fined and, refusing to pay, imprisoned.

In December 1914 the first of many articles demanding an end to the war was printed in Lansbury's Herald, then a weekly, whose anti-war stance had been muted since the war's outbreak.

The war against the war, conducted in part through the Herald, the Labour Leader and through the smaller circulation The Socialist, Sylvia Pankhurst's Women's Dreadnought (later Workers' Dreadnought) and, from 1916, the British Socialist Party's The Call, stopped only when the war stopped.

In his Left Book Club classic World Politics in 1936 the long-term editor of Labour Monthly and staunch anti-imperialist Rajani Palme Dutt, who also edited the Star's predecessor the Daily Worker from 1936-8, was to write: "All the calculations of the rival statesmen and general staffs were defeated by the event, and the war was rapidly revealed as an independent force which had passed beyond all possibility of control.

"Every imperialism was staking its all upon victory."

Dutt himself was imprisoned in 1916 for refusing conscription.

The war had an outcome, Dutt added, which was not anticipated by these statesmen. "The Russian revolution ended the war in the east. The German revolution ended the war in the west."

And by 1918 the empty pretence that the British government's motive for war was an altruistic wish to stand honourably by an ancient commitment to defend Belgium was exposed further by the Lenin government's publication of secret treaties made during the war between Britain, France and Russia.

Under these agreements Britain was to have southern Iraq, France was to have the seaboard of Syria and both were to share Palestine through a "protectorate."

Thus Iraq, Syria and Palestine, unlike Belgium, were not to be "saved" and were designated as appetising dishes to which the world's foremost imperialists could freely help themselves.

To treat a conflict born of clashing imperialisms, as Cameron's nasty capitalism-and-war-forever government is doing, as an opportunity for nationalist self-congratulation is an insult to history.

But we should remember the vastness of the human tragedy for people of many nations, and we should remember too, with respect and admiration, the efforts of socialists and progressives first to prevent it and later, their efforts to bring it to an end.