In the midst of deepening austerity, David Cameron is desperate to play the national card. Any one will do. He's worked the Queen's jubilee and the Olympics for all they're worth. Now the prime minister wants a "truly national commemoration" of the first world war in the runup to 2014 that will "capture our national spirit … like the diamond jubilee".

So £50m has been found to fund a four-year programme of events, visits to the trenches from every school and an ambitious redevelopment of the Imperial War Museum. Ministers have promised there will be no "jingoism", but Cameron says he wants to remember those who "gave their lives for our freedom" and ensure that "the lessons learned live with us for ever".

In case there were any doubt about what those lessons might be, the Times has declared that despite the war's unhappy reputation, Britain's cause was "essentially just", a necessary response to aggression by a "xenophobic and anti-democratic" expansionist power (Germany) and that those who fought and died did so to uphold the "principle of the defence of small nations".

It surely must be right to commemorate what was by any reckoning a human catastrophe: 16 million died, including almost a million Britons. It touched every family in the country (and many other countries besides), my own included. Both my grandmothers lost brothers in the four-year bloodletting: one in Passchendaele, the other in Gaza.

Seventy years after the event, one of them would still cry at the memory of the postman bringing the death notice in a brown War Office envelope to her home in Edinburgh. My grandfather was a field surgeon on the western front, who would break down as he showed us pictures he had taken of lost friends amid the devastation of Ypres and Loos, and remembered covering up for soldiers who had shot themselves in the legs, to save them from the firing squad.

But it does no service to the memory of the victims to prettify the horrific reality. The war was a vast depraved undertaking of unprecedented savagery, in which the ruling classes of Europe dispatched their people to a senseless slaughter in the struggle for imperial supremacy. As Lenin summed it up to the Romanian poet Valeriu Marcu in early 1917: "One slaveowner, Germany, is fighting another slaveowner, England, for a fairer distribution of the slaves".

This wasn't a war of self-defence, let alone liberation from tyranny. As the late Eric Hobsbawm sets out in his Age of Empire, it was the cataclysmic product of an escalating struggle for colonial possessions, markets, resources and industrial power between the dominant European empires, Britain and France, and the rising imperial power of Germany seeking its "place in the sun". In that clash of empires, Europe devoured its children – and many of its captive peoples with them.

Set against that all-destroying machine of 20th century industrial warfare, the preposterous pretext of the rights of small nations and the violated neutrality of "plucky little Belgium" cannot seriously be regarded as the real driver of the war (as it was not by British and other politicians of the time).

All the main warring states were responsible for the brutal suppression of nations, large and small, throughout the racist despotisms that were their colonial empires. In the years leading up to the first world war an estimated 10 million Congolese died as a result of forced labour and mass murder under plucky Belgian rule; German colonialists carried out systematic genocide against the Herero and Nama peoples in today's Namibia; and tens of millions died in enforced or avoidable famines in British-ruled India, while Britain's colonial forces ran concentration camps in South Africa and meted out continual violent repression across the empire.

The idea that the war was some kind of crusade for democracy when most of Britain's population – including many men – were still denied the vote, and democracy and dissent were savagely crushed among most of those Britain ruled, is laughable. And when the US president, Woodrow Wilson, championed the right to self-determination to win the peace, that would of course apply only to Europeans – not the colonial peoples their governments lorded it over.

As the bloodbath exhausted itself, it unleashed mutinies, workers' revolts and revolutions, and the breakup of defeated empires, giving a powerful impetus to anti-colonial movements in the process. But the outcome also laid the ground for the rise of nazism and the even bloodier second world war, and led to a new imperial carve-up of the Middle East, whose consequences we are still living with today, including the Palestinian tragedy.

Unlike in 1940, Britain wasn't threatened with invasion or occupation in 1914, and Europe's people were menaced by the machinations of their masters, rather than an atavistic tyranny. Those who died didn't give their lives "for freedom"; they were the victims of an empire that was a stain on humanity, the cynicism of politicians and the despicable folly of the generals. As Harry Patch, last British survivor of the trenches who died three years ago, put it, the first world war was "nothing better than legalised mass murder".

Since the 1990s, direct conflict between great powers that reached its cataclysmic nadir in the world wars has been replaced by a modern version of the colonial wars that preceded and punctuated them: in Iraq, Afghanistan and elsewhere. Unable to win public support for such campaigns, the government has tried to appropriate the sympathy for the troops who fight them as a substitute: demanding, for example, that poppies be worn as a "display of national pride" (or as Lieutenant General Sir John Kiszely, the now ex-British Legion president, described Remembrance Day, a "tremendous networking opportunity" for arms dealers).

If Cameron and his ministers try the same trick with the commemoration of the 1914-18 carnage, it will be a repulsive travesty. Among the war's real lessons are that empire, in all its forms, always leads to bloodshed; that state violence is by far its most destructive form; that corporate carve-ups fuel conflict; and that militarism and national chauvinism are the road to perdition. Celebrate instead the internationalists, socialists and poets who called it right, and remember the suffering of the soldiers – rather than the cowards who sent them to die. Attempts to hijack the commemorations must be contested every step of the way.

Seumas Milne's book, The Revenge of History: The Battle for the 21st Century, was published last week