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

In 1944, the United States was hoping for peace. Since 1914, it had fought in two major world wars. More than 500,000 Americans had died. Elsewhere in the world, over 100 million people had also lost their lives.

Today, there are many wars around the world. We need to figure out how to achieve lasting peace. Can studying the twentieth century’s global conflicts help us avoid future wars? Can it bring us closer to peace? We hope so.

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 terrible consequences of these wars.

The First World War

The First World War is an example of a war that didn’t have to happen.. There is no agreement on just what caused the war. Different historians have different ideas. Some say it was caused by the killing of an Austrian archduke. Others say it was the product of trends from the nineteenth century, such as nationalism and imperialism. Still others say the war was an accident. They claim it was sparked by misunderstandings between countries and a series of bad decisions.

Once we’ve investigated the war’s origins, we’ll explore the way it spread. While it started in Europe, it quickly became a global war.

Next, we’ll examine the wartime experiences of various people. We’ll also investigate the very different views of two women. One is the German antiwar activist Rosa Luxemburg. The other is 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 unexpected outcomes of the war. These outcomes include the Russian Revolution and the mass killing of the Armenian people.

Interwar

The First World War ended in 1918. Many world leaders were very eager to prevent another war. But just 20 years later, an even worse war broke out. What went wrong? That’s the question we ask in the second part of this unit. We will focus on the years between the two wars (1919–1939). These years are known as the Interwar Period.

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. These movements achieved little, however, and quickly fizzled out. This caused many people to lose their faith in democracy. As a result, extreme nationalism emerged once again. This nationalism took many forms. Of these, fascism was the most dangerous. It mixed extreme nationalism with racist beliefs and anti-Semitism. It called for violence and demanded obedience. Fascists and people with similar 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 began to seize territory in China and other nearby countries. The international community failed to put a stop to this. 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. Finally, in 1939, Britain and France warned Germany not to invade Poland. When Germany did invade, Britain and France declared war. The Second World War then 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 the Holocaust, 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. These two types of conflict were linked to each 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 tried to throw off the empires that ruled them. In places like Cuba, Vietnam, and Korea the two types of conflicts combined. This led to bloody, long-lasting wars.

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. In particular, we will focus on 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. And learning about these conflicts may just help us achieve lasting peace.