Two years ago this month, there were 24 left. Now, they are all gone, and there is nobody alive who fought in the First World War.

Well, there is still Jack Babcock, who joined the Royal Canadian Regiment in 1917 but got no closer to the fighting than England. And American veteran Frank Buckles, who drove an ambulance in France as a 17-year-old in 1918.

But the last real combatant, Harry Patch, who was wounded at the Battle of Passchendaele in 1917, died on Saturday (July 25).

They’ve been going fast. Erich Kaestner, the last German veteran, died in January 2008. Tony Pierro, who fought with the American Expeditionary Force in France in 1918, died in February. Lazare Ponticelli, the last of the generation of French men who fought in the trenches, died a month later. (One-third of French males who were between 13 and 30 in 1914 did not survive the war.)

Yakup Satar, who joined the Turkish army in 1915 and fought in Iraq, died in April 2008. Delfino Borroni, the last Italian veteran, died in October. Australia’s last veteran, Jack Ross, died last month, and Henry Allingham, the grandest old man of all, died a week ago.

Allingham was almost 20 in 1916 when he took part in the Battle of Jutland, the last and greatest clash of armoured steel battleships. (He saw the giant shells “skipping off the water.") As a mechanic in the Royal Naval Air Service, he flew missions over the freezing North Sea in 1917 in seaplanes that he described as “motorized kites”. And he spent 1918 in France trying to recover British planes that came down in No Man’s Land.

"We were moving forward at night,” he recalled about the Western Front. “It was dark... I fell into a shell hole. It was full of arms, legs, ears, dead rats--a lot of dead, rotten flesh... I lay there in the dark, not daring to move, cold and with my uniform stinking. I was frightened."

Sixty million men had the same memories, but they are no longer with us.

Harry Patch was an apprentice plumber when he was conscripted in 1916, and 19 years old when he arrived at the Western Front in 1917. He lasted four months before a German shell burst overhead, killing three close friends and wounding him in the groin. He was evacuated to England, and never saw the war again.

He married in 1918, had children, followed his trade of plumbing, and served as a volunteer fireman during the bombing raids on Bristol during the Second World War. He died on Saturday, at the age of 111.

So what have Harry Patch of Somerset and his 60 million comrades (for it no longer matters which side they were on) left behind for us?

One thing they would have been quite clear about: we can’t do this any more. In the First World War we crossed a threshold. All the advances in science and technology came together and created a kind of industrialized warfare that is simply unsustainable in human terms. It consumes soldiers, civilians, and whole cities at a rate that endangers civilization itself.

All the technological innovations that have been added since the First World War–armoured divisions, bomber fleets, nuclear weapons–only deepen the lesson, they don’t change it. Human beings have fought wars since we were all hunter-gatherers, and those who were good at it tended to prosper. Now, if you are really good at war, you will be destroyed.

Europe is just where industrialized total war first appeared. You can send expeditionary forces into the weaker parts of what we used to call the Third World and bash them to your heart’s content, but if you get into a serious fight with another fully industrialized country, you will be both be destroyed. (This is a lesson that emerging industrial countries like India, China, and Brazil can learn cheaply from history, or very expensively from experience.)

What else did the 60 million leave us? Inscribed on the wall of the chapel at the Royal Military Academy Sandhurst, where I taught “war studies” as a much younger man, is the first line of Horace’s poem, “Dulce et decorum est pro patria mori”: How sweet and fitting it is to die for one’s country. But we don’t believe that lie any more.

Wilfred Owen was killed crossing the Sambre canal a week before the war ended. He never got any older than 25, but he put the wisdom that the millions bought with their lives into his poem “Dulce et decorum est.” It’s about a poison gas attack, and the last lines run: If you could hear...the blood come gargling from the froth-corrupted lungs...My friend, you would not tell with such high zest to children ardent for some desperate glory, the old Lie: Dulce et decorum est pro patria mori.

It’s almost a century now since anybody but fascists and fools saw war as glorious. The government may tell us that our “glorious dead” have “fallen”, but we know that they were only teenagers, and that they died in agony and lost all the rest of their lives. Sometimes, we even worry about the fact that we have sent them to kill people for us.

In 1917, during the Third Battle of Ypres, Harry Patch was manning his machine-gun when a German got close enough that he looked like a real person–and suddenly Harry realized that he didn’t want to kill him. Shouldn’t kill him, in fact. He shot the German in the shoulder, which made him drop his rifle, but he kept coming.

So Harry shot him again, first above the knee and then in the ankle. God knows if the German survived all this, but at least Harry was trying. So are the rest of us. Most of the time.

Gwynne Dyer’s latest book, Climate Wars, was published recently in Canada by Random House.