​The "War to End All Wars," 100 years later

Nearly a century ago, Corporal Martin Berger, from the Bronx, N.Y., went into battle in France. He was one of the lucky ones who came home from "the Great War." Martha Teichner looks back at what was supposed to be "the war to end all wars":

True story: On Sept. 7, 1914, exactly 100 years ago today, 600 taxis, commandeered from the streets of Paris, shuttled 6,000 reinforcements to the battlefield -- soldiers who, by many accounts, made all the difference. The French and British defeated the Germans at the First Battle of the Marne.

Two million men fought each other there. In just a week of battle, there were an estimated half a million dead and wounded.

World War I was barely a month old, but already the kind of war it would be was becoming evident.

"In absolute numbers, this war defies previous understandings of war, and then defines future expectations of war," said Oxford professor Sir Hew Strachan, one of the world's most noted WWI scholars.

"The lesson from this war still is that what we want to do is try and avoid war," said Strachan. "And the sense of the loss of life that comes from it derives precisely from 1914-18.

It began with an isolated act of terrorism. On June 28, 1914, in the Bosnian capital of Sarajevo, the heir apparent to the Austro-Hungarian throne, Archduke Franz Ferdinand, and his wife, were shot by a Serbian nationalist.

How did the assassination of an obscure archduke lead to a world war?

Strachan said it was a system of collective security in place, "which makes it very hard for any one state to stand back without compromising its own security."

On July 28, Austria-Hungary, one of the world's great powers, declared war on Serbia. Serbia asked its friend, Russia, for help. Then, Austria-Hungary turned to its friend, Germany.

Germany had its own agenda -- it wanted to invade France, but getting there meant invading Belgium, too. So Britain -- committed to supporting Belgium, France and Russia -- declared war on Germany.

And that, Strachan said, produced a snowball effect: "It becomes a world war because many of these powers are colonial powers as well as being European powers."

Like dominoes, country after country was dragged in -- on the side of the Allies, or the Central Powers -- until practically the whole world was at war.

But not the United States, which remained neutral . . . at first.