On August 8, 1918 — 100 years ago last Wednesday — it finally became clear who was going to win World War I.
Nine Canadian and Australian divisions, almost 200,000 men, attacked the German trenches near Amiens, deep in France — and for the first time in the war, the German troops ran away.
By the second day of the battle the Germans were resisting fiercely again, but the German commander, General Erich Ludendorff, called it "the black day of the German army".
After that Germany did nothing but retreat, and the armistice was signed only three months later.
Yet just a few months before, Germany nearly won the war.
The Bolshevik Revolution took Russia out of the war in 1917, and Germany was able to shift half a million troops to western Europe.
For the first time it had numerical superiority over the British and French troops, and the great German offensives of spring 1918 tore the old Western Front apart.
But the German offensives ran out of steam without permanently splitting the French and British armies, and the war might have ended there — in a draw.
Everybody was exhausted by 1918, and half the French army had mutinied in 1917 and was still not fit for combat, while British divisions were down to half their strength.
Only the Canadians and the Australians still had full-strength divisions (up to 25,000 men), and they were very experienced troops by 1918. That's why they spearheaded almost every attack in the "Hundred Days" offensive that ended the war.
But the real reason German morale collapsed was that 10,000 more American troops were landing in France every day.
That's the real history, and the result was a catastrophic defeat for Germany and a peace treaty so harsh that it laid the foundations for the rise of Adolf Hitler and a second — even worse — world war.
But change only one decision, and it could all have come out very differently.
That decision was taken in January 1917.
At that point there seemed no way for Germany to beat the far larger numbers of its enemies on the battlefield, and a German admiral persuaded the government to launch unrestricted submarine attacks on ships bringing supplies to Britain — including ships of neutral countries like the United States.
That would bring America into the war, of course, but the admiral promised that Britain would be starved into making peace long before any American troops reached Europe.
He was wrong — Britain didn't starve, and the United States declared war on Germany in April 1917. By mid-1918, US troops were flooding into France, and the game was up.
Timing is everything. The Russian revolution happened just after Germany decided on unrestricted submarine warfare — if that decision had been delayed by only two months,
Berlin would have known that Russia was probably going to leave the war and they would never have taken the desperate gamble that the admiral was urging on them.
The German U-boats would never have sunk American ships, the US would have stayed out of the war ... and Germany might have won in 1918.
That would have been a good thing, because Germany would not have won a huge, decisive victory. It would just have won on points: "Okay, our spring offensives didn't succeed, but our troops are standing up to your counter-offensive (no masses of American troops to demoralise them). So maybe we should all just quit and go home."
There would have been no "peace" treaty like Versailles that heaped all the blame for the war on one side and made the losers pay the entire cost of it ("reparations").
Germany would presumably have got its colonies back, but no territory would have changed hands in western Europe. And there probably would not have been World War II.
Hitler came to power because Germany was punished so severely for a "war guilt" that was really a shared responsibility.
A "no-score draw", by contrast, could have focused people's attention more sharply on the basic lunacy of an international system that fostered such wars.
By the turn of a coin we got the 20th century that's in the history books, instead.
Too bad ... it's hard to think of a different 20th century that would have been worse.
Gwynne Dyer's new book is "Growing Pains: The Future of Democracy (and Work)"