Young people should be more interested in peace than anybody else. As former president Herbert Hoover said in 1944, “Older men declare war. But it is the youth that must fight and die.”

Hoover was speaking at a time when the country was hoping for peace. Twice in just 30 years, the United States had joined at least half the world in marching its young men (and increasingly, young women) into modern warfare’s hail of bullets, bombs, and artillery shells. From 1914 to 1945, more than 500,000 Americans were killed in two world wars. Elsewhere in the world, over 100 million other human beings also fell victim to these wars.

Many of you, today, may be looking at the wars going on around us, wondering how they will affect you and how the world can achieve peace. Can studying history—and in particular the global conflicts of the twentieth century—help us avoid a repetition of the horrors of the past? Can it bring us closer to peace?

In this unit, we approach this question through two kinds of lessons. In some, we seek to understand the causes of three twentieth-century conflicts: the First World War (1914–1918), the Second World War (1939–1945), and the Cold War (1945–1991). In other lessons, we try to describe the human experiences and the terrible cost of these wars. We hope that by examining these global conflicts we can learn lessons that will positively affect the future.

The First World War

The First World War is a tragic example of a war that didn’t have to happen. It’s a warning about how many small factors can combine to trigger massive destruction. We begin this unit by looking at debates surrounding the origins of the First World War. Was the war caused by an assassin’s bullet that found its target in an Austrian archduke in Sarajevo? Or was it a product of longer, darker trends from the nineteenth century, such as nationalism and imperialism? Or was the war an accident—sparked by a series of bad decisions and miscommunications between countries in the key months of July and August 1914?

Once we have investigated how the war began, we’ll explore the experiences and outcomes of the war. We’ll look at how a conflict that started in Europe in 1914 became a global war, affecting people as far away as Southeast Asia and the Middle East.

Next, we’ll explore the experiences of individuals who fought in and lived through the war, like the Indian soldiers serving Britain in the image above. We’ll see how their experiences changed the way they saw the world around them. We’ll also investigate the very different perspectives of two women: the German antiwar activist Dr. Rosa Luxemburg and the American volunteer nurse Helen Fairchild.

Finally, we’ll consider how whole societies were transformed by what was perhaps the first “total” war in history. We’ll focus on the “lost generation” of young people who came of age during the war. And we’ll also examine some unanticipated outcomes of the war, such as the genocide of the Armenian people and the Russian Revolution.

Interwar

When the First World War ended in 1918, many world leaders hoped to prevent another war. Instead, just two decades later, an even larger and more devastating war broke out. What went wrong? That’s the question we ask in the second portion of this unit, which focuses on the Interwar Period (1919–1939).

We’ll begin by looking at a shared experience that deepened the sadness and suffering after the war: the great economic depression of the 1930s. This lesson examines how economies and people around the world had become more interconnected than ever, which meant that when one economy collapsed, others soon followed.

In another lesson, we’ll see how movements for international cooperation and peace briefly flourished in the 1920s, but then quickly fizzled out. After seeing how international cooperation failed to solve the world’s problems, many people lost their faith in democracy. As a result, extreme nationalism emerged once again, more powerfully than before the First World War. This nationalism took many forms, including racism and anti-Semitism. But perhaps the most menacing element was the rise of fascism, a set of ideas that mixed extreme nationalism and racist beliefs with a call for violence, action, and obedience. Fascists and people with similar ideas emerged in many places, including the United States. In a few countries, in particular, Italy, Japan, and Germany, fascists and authoritarians managed to seize power.

The Second World War

In the 1920s, Japan’s authoritarian government began to seize territory in nearby countries—mostly China—and the international community failed to stop them. In the 1930s, Fascists in Italy and Nazis in Germany invaded their weaker neighbors in Europe and North Africa. Again, nobody was willing to stop them. Germany kept pushing the limits until, in 1939, Britain and France warned Germany not to invade Poland. When Germany did invade, Britain and France declared war, marking the start of the Second World War.

These lessons look at the origins of World War II and the experiences of those who lived through it. In one lesson, we’ll explore how the Second World War began, and how the international community failed to stop it. In another, we’ll look at the human cost of the war in terms of death and destruction. In a third, we’ll look at the experiences of Jewish communities and others targeted by the Nazis in the mass murder known as the Holocaust. Finally, we’ll discuss the dropping of nuclear bombs on the Japanese cities of Hiroshima and Nagasaki in 1945.

Cold War and Decolonization

Despite the Holocaust and the mass suffering of civilian populations around the world, the world didn’t suddenly enter a period of peace following the end of the Second World War. Instead, two new types of conflicts emerged, each linked to the other. One was the global struggle between two nuclear-armed superpowers—the United States and the Soviet Union—and their allies. Because they could destroy each other, these two sides mostly avoided large-scale warfare. Instead, they fought a “Cold War” of smaller conflicts and regional wars. The other type of conflict consisted of wars of decolonization, in which colonies sought to throw off the empires that ruled them. In a series of wars in Cuba, Vietnam, Korea, and elsewhere, these two types of conflicts combined to produce bloody, long-lasting battles.

In these lessons, we’ll look at the causes of the Cold War and decolonization conflicts, as well as the experiences of people who lived through them. In one lesson, we’ll see how the end of the Second World War produced these conflicts. We will then look at the origins of the Cold War and the experiences of people who lived through the arms race and space race that contributed to it. We will also explore communism, and in particular the origins and experiences of the Chinese Communist Revolution that brought to power the current government in China.

In other lessons, we’ll examine decolonization, and the different paths it took in various colonies. One lesson focuses on decolonization as it relates to human rights. This lesson addresses gender, especially women’s roles in decolonization.

The Cold War ended in 1991. But in many ways, the conflicts that are the focus of this unit shaped the world we live in today. It’s worth studying them to see how today’s world was made and to give us ideas about how we might make a conflict-free world in the future.