Soon after the end of the First World War, great dictatorships began to take shape which, born out of the ashes of one conflict, encouraged, if not provoked, another, far more catastrophic one: Nazism in Germany, fascism in Italy, militarism in Japan and communism in the Soviet Union.

In Germany, Adolf Hitler capitalised on the German people's social resentment and dissatisfaction with the humiliating Treaty of Versailles, inflation and economic depression by promising to reunite "Greater Germany" by restoring it to the role of a great military power. But he was to have absolute control over the nation. Hitler became leader of the National Socialist German Workers' Party on 24 February 1920. He assumed full power on 14 July 1933. Hitler's strategic plan was to establish a new European order by creating a strong empire through the occupation of territories to the south and east of Germany. After occupying France and using air power to force Britain to sue for peace, he would turn to the Soviet Union to conquer what Hitler called Lebensraum, the agricultural lands of the Ukraine, the oil wells of the Caucasus and, at one point, flirting with the idea of joining forces with the Afrika Korps at the Suez Strait.
This would have changed the entire geopolitics of the Middle East and the Mediterranean, to the total detriment of Britain's Central Asian possessions.

Benito Mussolini founded the Fascist Party in Italy on November 9, 1921, and became prime minister on October 31, 1922. In January 1925, he assumed de facto dictatorial powers. He capitalized on discontent over the "mutilated victory" of the Treaty of Versailles and promised the Italian people that he would restore Italy to its former greatness. Following the example of the Libyan colony, Italy invaded Ethiopia in pursuit of expansion in East Africa. With Italy's entry into the war, Mussolini hoped to capitalize on the successes of the German army to gain territory for himself. However, the weakness of the military structure was quickly exposed on the northwestern border with France, as well as in the subsequent campaigns in North Africa and Greece. There, Mussolini was forced to ask Hitler for help. Between 1936 and 1939, Hitler and Mussolini sent substantial military forces to Spain in support of Francisco Franco, helping him seize power and establish a dictatorship similar to those in Italy and Germany. For the German Wehrmacht, it was an opportunity to try out new tactics and military equipment, including aircraft and tanks produced in Germany as a result of the massive rearmament program the Nazis had unilaterally decided on since 1935. No Allied power had taken a stand against this program during the First World War.

General Hideki Tojo represented Japan's militarism. A career soldier, he served as Minister of War from July 1940 to July 1944 and as Prime Minister from October 1941 to July 1944. His fierce determination and uncompromising expression of the extremist tendencies of the military caste led to the downfall of the moderate government and the triumph of the bellicose tendency. On October 17, 1941, he formed a new government and assumed the presidency as well as the ministries of War and the Interior.

On September 18, 1931, Japan invaded the Chinese region of Manchuria. In 1932, Japan began invading China. That same year, Japan withdrew while launching a campaign to blockade China's economy. Fighting resumed in July 1937, and by 1938, the Japanese Empire had completed its economic blockade of China by controlling its ports, industries, and railway hubs.

The start of the war in Europe gave the Japanese an opportunity to extend the war to Southeast Asia through what they called the "Great East Asian Co-Prosperity Sphere," contingent on the defeat of the U.S. Pacific Fleet.

In the Soviet Union, Joseph Stalin, who succeeded Lenin after his death in 1927, ruled with an iron fist. He persecuted opponents and promised a dictatorship of the workers' party.
One of the terrible purges of the 1930s was the one in which 35,000 out of 144,000 Red Army officers were sentenced to death or imprisonment.

This, together with Stalin's initial indecision, caused the German army to advance recklessly during Operation Barbarossa. This invasion of the Soviet Union began on June 22, 1941, resulting in millions of casualties.

The Non-Aggression Pact, signed on August 23, 1939, defined the spheres of influence of the Third Reich and the Soviet Union in areas near each other.

Stalin's goal was to establish buffer zones between the two countries. Polish territory was divided between the Soviets and the Germans, and the Red Army occupied the Baltic republics.