The Great War, as it came to be known, lasted four years, from 1914 to 1918. But its aftereffects haunted Europe and the rest of the world through the 20th century—and are still felt in our own times.

In this groundbreaking book, British historian David Reynolds ranges far and wide across economics, poetry, diplomacy, and politics to tease out the complex consequences of what was hoped to be "the war to end all wars" but instead became the precursor of World War II and numerous other conflicts, including the war in Iraq.

Here Reynolds talks about how women's lives were changed by the conflict, how Woodrow Wilson's policies led to the rise of America as a global power, and why it's crucial to look beyond the myths that have shaped our perception of World War I.

Tomorrow is the hundredth anniversary of the outbreak of the Great War. Why did you call your book The Long Shadow?

Because I think the Great War does cast a long shadow over the 20th century. George Kennan, the American historian and diplomat, called it the seminal conflict of the 20th century. The Germans' historians have called it the Ur-Katastrophe, the original catastrophe. So I think that in a variety of ways I try to explain [that] this is a war that we're still living with in terms of its legacies.

The war resulted in the collapse of two empires. What were the consequences of this? Particularly in the Middle East?

I would say that three big empires collapsed, if you think of the Romanov [Russian] empire, the Habsburg empire, and the Ottoman Empire, which still had control over a large area of the Middle East. It is fighting the Russians in the Caucasus. It is fighting the British around the Mediterranean. The British gradually conquer what became Palestine, and what is called Mesopotamia, at the time but becomes the state of Iraq. Those are areas that are hugely controversial all through the 20th century and remain so now. If you think of the fraught relations between Arabs and Jews. If you think of the patched-up state of Iraq. These are fundamental issues in our newspapers today.

One of your aims in the book is to dispel some of the myths about World War I. What are those myths?

Every country has its own great war, so part of what I am trying to do is to explore different countries' takes on 1914-18. The one I am particularly focused on is the British point of view, and the British view of the war is stuck in the trenches and trapped in Poets' Corner—meaning that the British mostly think of the First World War as a story of mud and blood along the Somme, a war that is static and goes nowhere, a war in which the tragedy of ordinary soldiers is understood through war poets like Wilfred Owen, a poet who is hardly known outside Britain but who is fundamental to the English school curriculum.

Though it was geographically distant from the conflict, the United States was also deeply affected by the Great War.

In 1914 the U.S. is a neutral country. Woodrow Wilson, the president, stands aloof from the conflict, not least because he is very conscious that the increasingly ethnically pluralist population of the U.S. is almost a microcosm of the warring powers in Europe. You've got a lot of people of British ancestry, who are fervently supporting Britain. And you've got a lot of people of German ancestry. Wilson says that the best position for the U.S. is neutrality so that the war will not spread to American soil in the form of civil strife. He also argues that it is an imperialist war, the sort of thing that the Europeans have been doing for centuries and the New World should take a principled stance against.

But the problem for the U.S. is that it is economically so important to the belligerent powers that the position it takes economically, as distinct from politically, becomes a major factor in the war. America's economic ties are overwhelmingly with Britain, and so what develops is an economic bias toward Britain, which is in tension with Wilson's political stance of neutrality.

That's an issue which becomes fundamental to the Germans by the winter of 1916-17, when the war is deadlocked on the land front. The Germans start unrestricted U-boat warfare to cut Britain's lines of communication with the U.S. It's an act of desperation and a breach of international war. And it's what ultimately pushes the U.S. into the conflict in April 1917. Its new position as the arbiter of world affairs is the start of America's rise to global supremacy in the 20th century.

America was also the biggest economic beneficiary of the war. America before the war is a net debtor in international currency flows, to the tune of $3.7 billion. Rather neatly, by the end of the war it is a net creditor of $3.7 billion.

Perhaps partly because you are a British historian, it's the British experience that is at the heart of the book. Britain came out of the conflict with its empire enhanced. The war also forged a new sense of British identity. Can you unpack those two things?

The British Empire grows to its largest extent as a result of the war of 1914-18. Particularly in terms of its new possessions in the Middle East, like Iraq and Palestine, which prove to be something of a poisoned chalice but are big assets for the British at the time. In the case of Iraq, the British get access to crucial new resources, like oil.

The empire grows in another way. One of the distinctive things about it was the so-called settler colonies—where people of British stock have gone abroad and established their own colonies, usually at the expense of native populations—like Australia, New Zealand, Canada, and South Africa. These "dominions" were extremely important to the war effort and again in the Second World War. And that sense of a British world, or Commonwealth, was a very powerful addition to Britain's capabilities. The Indian Army contributes something like one million men to the British Army in World War I, and they become part of the story.

The way the war dead were commemorated varied greatly from nation to nation and says a lot about the cultural values of the combatants, doesn't it?

In previous wars, certainly 19th-century wars, dead soldiers had been basically thrown into anonymous mass graves. But we are now in a democratic era in which, at least officially, each person is counted equally in politics and in society. The powerful feeling among the older men, who have in a sense sent the younger men to war, is that these young men should be recognized and honored. It would be far too expensive to bring the soldiers back: We're talking about 720,000 dead. Instead, you bury them with honor where they fell, and you also ensure that each grave has the man's name attached to it. So all along the western front, for almost a hundred miles, you have this necklace of war cemeteries, beautifully kept up by the Imperial War Graves Commission. The British are honoring their dead in what Rupert Brooke called "a foreign field that is for ever England," and that's part of the poignancy of the British commemoration.

Rudyard Kipling was very active in promoting the concept of the war graves—and there's a reason for that, isn't there?

Kipling was involved in the planning of the war cemeteries and in particular in some of the language that was used. He's the originator of a very poignant phrase for soldiers whose bodies had been found but were never identified: "Known Unto God." Kipling felt deeply about this because he had sent his only son, Jack, into the war. Jack had very bad eyesight and could easily have gotten a medical exemption. But he wanted to fight, and his father wanted him to fight. Jack was last seen on the battlefield of Loos in 1915 with half his face shot off. His body was never found during Kipling's lifetime. It's possible that he's now been found, but that's disputed. And I think he sublimated his guilt in this process of war commemoration in a way that is very, very sad.

We've talked so far mostly about men, but the Great War also had a decisive effect on women, didn't it?

The war changes the terms of the debate. Because a lot of women take on men's jobs, in the factories or running the trams. Eight hundred thousand women work in munitions factories. They are known as "Tommy's Sister." Tommy is the soldier on the front. Tommy's Sister helps him by producing essential supplies like munitions, guns, food that are necessary for an era of what is called "total war." In other words, a war that involved the home front as much as the battlefield. So a lot of politicians who are violently opposed to suffrage in 1914 have to admit that men who fought, and women who have done war service on the home front, have shown their right to citizenship.

It was called "the war to end all wars," but that didn't happen. In 1939 Europe was at war again. How much did the Second World War grow out of the legacy of 1914-18?

In significant ways the war that began in 1939 grows out of the unresolved issues of 1918. Above all, Germany thinks that it had been put in a subordinate and humiliating position in Europe, which was unacceptable. So the German desire for revenge and for reviving its international position was central. Equally, you have a situation in Eastern Europe where you have these various small and not viable new states with disputed borders and minority problems. It's no accident that the big crisis of 1938 is over Czechoslovakia and the German minority there, plus Poland, which is disputed between Russia and Germany. Hitler's ambition is the fire for the new conflict. But the fuel for the Second World War is this tinderbox in Eastern Europe.

What was the most moving part of your research?

I think the part that I found most moving to write was the chapter called "Civilization," which is where the devastation and loss of life of this appalling conflict is understood through poetry and art. It is an attempt to reflect and add meaning—and in a strange way a sense of beauty—to something that was grotesque and appalling. And that struggle, which is what art is about, seemed to me particularly poignant in the case of this conflict.

The BBC and other British institutions, like the Imperial War Museum, are investing enormous resources in centenary commemorations. What do you hope will be achieved?

My hope is that the centenary is going to be not just an act of remembrance for the dead but also an opportunity to understand the 1914-18 war in terms of its broader impact on the home fronts and on the wider world—to move it from simply remembrance to trying to understand this appalling conflict, which fundamentally shaped the century that followed, and in some ways still shapes the world we live in now.