Nobody should be more interested in peace than young people. As former president Herbert Hoover told the Republican National Convention in 1944, “Older men declare war. But it is the youth that must fight and die.”

Hoover was speaking in a country that 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 the hail of bullets, bombs, and artillery shells of modern warfare. From 1914 to 1945, more than 500,000 Americans died in the two world wars, joining over 100 million other human beings as casualties of these two 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 repeating the horrors of the past and 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 terrible cost of these wars. We hope that by examining what caused the global conflicts of the twentieth century, and by understanding the suffering they produced, we can learn lessons about war and peace 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 the evidence and 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 the war a product of longer, darker trends from the long nineteenth century, such as nationalism and imperialism? Or was the war an accident—sparked by a series of miscommunications and bad decisions 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. Through a series of videos, we’ll witness this war from the perspectives of people in different places, including Britain, Southeast Asia, and the Middle East.

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

Finally, we will consider how whole societies were transformed by what was perhaps the first “total” war in history. Our story here will take us to the peace talks in France where the future of the world was being debated, and to the “lost generation” of young people who came of age during the war. But we will 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? To answer that question, we’ll learn about the interwar period (1919–1939).

We begin by looking at a shared experience that deepened the sadness and suffering after the war—the great economic depression of the 1930s. In the period after World War I, the world rebuilt the connections linking people and economies. Unfortunately, that meant that when one economy collapsed, others soon followed.

During this same period, we’ll see how movements for international cooperation and peace briefly flourished in the 1920s but then quickly fizzled out, the result of many people losing their belief in democracy as they witnessed how international cooperation failed to solve the world’s problems. 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, an ideology that mixed extreme nationalism and racist ideology 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.

We will explore the origins of World War II and the experiences of those who lived through it. We will look at the human cost of the war in terms of death and destruction. We will discuss the cumulative effects of this war up to and including the dropping of nuclear bombs on the Japanese cities of Hiroshima and Nagasaki in 1945. Finally, we will encounter the experiences of Jewish communities and others targeted by the Nazis in the mass murder known as the Holocaust.

Cold War and Decolonization

Despite such horrendous atrocities as 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, and instead fought a “Cold War” of smaller skirmishes and regional wars. The other types of conflict were decolonization struggles, in which colonies sought to throw off the empires that ruled them. In a series of wars in Cuba, Vietnam, Korea, and elsewhere, Cold War and decolonization conflicts combined to produce bloody and protracted battles.

In these lessons, we look at the causes of these Cold War and decolonization conflicts as well as the experiences of people who lived through them. We will see how the end of the Second World War produced these conflicts. We then look at the origins of the Cold War and the experiences of people around the world who lived through this period of global competition between capitalist and communist alliances.

The Cold War ended in 1991, concluding the events covered in this unit. 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.