06/08/2014 13:01 BST | Updated 06/10/2014 06:59 BST

Imagining a World Without War

On Monday I attended two consecutive events that you might have expected to have delivered clashing messages.

The second, in Westminster Abbey, had a large and beautifully printed programme, with the title "A Solemn Commemoration on the Centenary of the Outbreak of the First World War". It was televised on BBC2, its 'star' was the Duchess of Cornwall and it was attended by thousands of people, a significant proportion of them in uniform. It was (mostly) the Establishment on parade.

The first was just outside the Abbey, on Parliament Square. It was far less formal - a small sound system and hundreds of people, some with placards, standing in the dusk. This was organised by the No Glory in War campaign, and there were few uniforms in sight - bar a WWI Tommy's helmet worn by political activist Chris Knight, who also carried a placard around his neck emblazoned with the words of World War I veteran Harry Patch, "War is nothing better than legalised mass murder."

Outside the Abbey there was a lot of thoughtful commentary around the theme of "no more war". German historian Juliene Haubold Stolle offered a reflection on her country's military history, with the observation that current attitudes to war are shaped by how we view past conflicts.

The Abbey ceremony wasn't so very different, much of its readings being drawn from World War I diaries and letters, including the diary of Georgina Lee, who on 30th July, 1914, had written: "Grave rumours of a possible terrible conflict of Nations are on everybody's lips", and Wilfred Owen reflecting on the result: the "great darkness closes in".

The contemporary reflection came from Sir Hew Strachan, Chichele Professor of the History of War at the University of Oxford, who said that we should understand, not judge, the leaders of 1914, who'd failed to keep the peace, understanding that our own world has a continuing engagement with war.

One of the readings was the entirely apt passage from Isaiah 2 about beating swords into ploughshares and spears into pruning hooks, imagining the end of war.

The tone of the ceremony contrasted with the words of Prime Minister David Cameron who, earlier on Tuesday, was keen to defend the decision to go to war in 1914, and tried to draw parallels to the current day.

Events of almost a year ago - the Commons vote against military intervention in Syria - do reflect a fundamental change in the British attitude towards war. As I said at the No More War event, the vote marks the most internationally significant event in the term of this government.

For after that vote, US President Barack Obama decided that he too needed Congressional backing for any action. The vote was the beginning of a process which looks to have consigned the doctrine of unilateral Western intervention, so disastrous in Afghanistan and Iraq, to the dustbin of history.

What we need to do now is go further. To not just mourn the horror of war, but try to imagine, and then create, a world without war.

With the hideous death-toll in Gaza, the chaos in Syria and Ukraine, the turmoil in Libya, that might seem a long way from the reality of 2014. But the important first step is to say "this is possible", and then to start to plan the actions needed to bring a peaceful world into being.

There are some obvious first steps.

One is to remove the remaining threat of nuclear war. With Trident replacement now on the horizon, there's huge potential for Britain to set an example, to lead the way, which is why I'll be at the CND Wool Against Weapons event on Saturday, Nagasaki Day.

And another is to stop pumping more weapons out into an over-armed world - the importance of which we were reminded of by the horrific fate of MH17. That Britain is still subsidising arms exports to Saudi Arabia, the human rights-abusing, clearly long-term unstable state, shows that we have not learned the lessons of Saddam Hussein, Colonel Gaddafi and so many other dictators we've armed and propped up over the decades.

Ultimately there is no justification for an arms export trade: the final costs, in human and economic terms, are way too high.

Again, Britain could lead the way - in following the hopes of Isaiah from the so long-distant past: turn the arms factories to constructive, peaceful purposes, and immediately improve the state of the world.

As we remember, in the coming years, the terrible toll of "the war to end all wars", rather than reflecting on the century of conflict that has followed, we can recommit to the aim of delivering the hopes of those fresh-faced young men we see in the photos marching off to fight in World War I.