Young people should want peace more 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. Since 1914, the United States had fought in two major world wars. More than 500,000 Americans died as a result. Elsewhere in the world, over 100 million other people also lost their lives.

Today, many of you may be looking at the numerous wars that are being fought right now. You may be wondering how the world can finally achieve peace. Can studying the global conflicts of the twentieth century help us avoid future wars? Can it bring us closer to peace?

There are two kinds of lessons in this unit. In some, we try 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 describe the human experiences and the terrible cost of these wars.

The First World War

The First World War didn’t have to happen. It’s a tragic example of how many small factors can combine to trigger massive destruction. We begin this unit by looking at debates surrounding the origins of the war. Was it caused by the assassination of an Austrian archduke? Or was it the product of trends from the nineteenth century, such as nationalism and imperialism? Or was the war an accident? Was it sparked by a series of bad decisions and miscommunications between countries?

Once we have investigated the war’s origins, we’ll explore the way it spread. We’ll look at how a conflict that started in Europe became a global war.

Next, we’ll examine the experiences of individuals who fought in and lived through the war. We’ll also investigate the very different perspectives of two women: the German antiwar activist Rosa Luxemburg and the American volunteer nurse Helen Fairchild.

Finally, we’ll consider how whole societies were transformed by the war. We’ll focus on the “lost generation” of young people. And we’ll examine some unanticipated outcomes of the war, such as the genocide of the Armenian people and the Russian Revolution. A genocide is a planned and organized attempt to destroy an entire people.

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 the great economic depression of the 1930s. This experience deepened the suffering of many people after the war.

In another lesson, we’ll see how movements for international cooperation and peace briefly took off in the 1920s, but then quickly fizzled out. Many people lost their faith in democracy when they saw how international cooperation failed to solve the world’s problems. As a result, extreme nationalism emerged once again. This nationalism took many forms, including racism and anti-Semitism. Fascism was the most dangerous new form of nationalism. It mixed extreme nationalism and racist beliefs with a call for violence, action, and obedience. Fascists and people with similar authoritarian ideas emerged in many places, including the United States. In a few countries, they managed to seize power. This was particularly true in Italy, Japan, and Germany.

The Second World War

In the 1920s, Japan’s authoritarian government began to seize territory in China and other nearby countries. 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. With that declaration, the Second World War began.

In one lesson, we’ll explore how the international community failed to stop the war. In another, we’ll look at the death and destruction the war caused. In a third, we’ll look at the mass murder campaign known as the Holocaust, during which the Nazis killed millions of Jews. Finally, we’ll discuss the dropping of nuclear bombs on the Japanese cities of Hiroshima and Nagasaki in 1945.

Cold War and Decolonization

Sadly, the world didn’t 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 and their allies. Those two superpowers were the United States and the Soviet Union. Because they could destroy each other, they mostly avoided large-scale warfare. Instead, they fought a “Cold War” of smaller battles and regional wars. The other main type of conflict was a series of wars of decolonization. Through these wars, colonies attempted to throw off the empires that ruled them. In a series of wars in Cuba, Vietnam, Korea, and elsewhere, the two types of conflicts combined. This led to bloody, long-lasting battles.

In these lessons, we’ll look at the causes of the Cold War and decolonization conflicts. 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 it. We’ll examine the arms race and the space race, which contributed to the Cold War. We’ll also explore communism and, in particular, the Chinese Communist Revolution.

In other lessons, we’ll examine decolonization. One lesson focuses on the relationship between decolonization and human rights. It also looks at women’s roles in decolonization.

The Cold War ended in 1991. But in many ways, the conflicts this unit discusses shaped the world we live in today. It’s worth studying them to see how today’s world was made. What’s more, learning about them may give us ideas about how we can achieve lasting peace.