During the political confusion of the early 1930's, the Nazi Party made rapid gains in German elections. The party had been founded in 1919. After its 1923 revolt failed, party leader Adolf Hitler decided to gain power by lawful means rather than by revolution. From 1924 to 1929, the republic was prosperous and stable, so the Nazis attracted few voters. After the Great Depression struck, more Germans were attracted to Hitler's promises to improve the economy, defy the hated Treaty of Versailles, and rebuild Germany's military power. In 1932, the Nazi Party emerged as the Reichstag's strongest party. In 1933, Hindenburg appointed Hitler chancellor.

Soon after he became chancellor, Hitler began to destroy the constitution and build a dictatorship. He permitted only one political party—the Nazis. The party seized control of the nation's courts, newspapers, police, and schools. People who opposed the government were murdered, imprisoned in concentration camps, forced to leave Germany, or beaten up by the Nazis' private army called storm troopers. After Hindenburg died in 1934, Hitler declared himself der Fuhrer (the leader) of Germany. The Nazis called their government the Third Reich (Third Empire). The first was the Holy Roman Empire, and the second was the German Empire.

Many Germans approved of Nazism. Many others objected to some features of Nazi rule, but supported Hitler's efforts to improve the economy and rebuild the military. Some Germans opposed Hitler but remained silent. Only a few resisted.

Hitler pursued two goals. He wanted to assert German superiority over what he believed to be inferior races, including Jews, Slavs, and other non-German peoples. He also wanted to gain territory—lebensraum (living space)—for Germany, especially in eastern Europe. In 1933, Hitler removed all German Jews from government jobs. In 1935, he took away the rights of Jewish citizens. Faced with this persecution, more than half of Germany's 500,000 Jews left the country. On the night of Nov. 9-10, 1938, Nazi crowds burned down synagogues and broke the windows of Jewish businesses in an event later called Kristallnacht (Crystal Night). In English, the event is known as the Night of Broken Glass.

At the same time Hitler was acting against the Jews, he was also preparing for war. In 1936, German troops reoccupied the Rhineland. Also in 1936, Germany formed an alliance with Italy and signed an anti-Communist agreement with Japan. The three countries became known as the Axis powers. In March 1938, Germany occupied Austria and made it part of the Third Reich. In September, the United Kingdom and France consented to Hitler's demands to take over the German-speaking areas of Czechoslovakia. The next year, Germany seized the rest of Czechoslovakia.

In August 1939, Germany and the Soviet Union (which had been formed under Russia's leadership in 1922 and existed until 1991) agreed to remain neutral if the other became involved in a war. They also secretly planned to divide Poland and much of the rest of eastern Europe between themselves. On September 1, Germany invaded Poland and World War II began.