World War II was fought between Axis Powers (Germany, Italy and Japan) against the Allies (Britain, USSR, USA, France). Let's understand this in detail.

Axis Powers
The Axis Powers were the countries that fought against the Allies during World War II. The Axis Powers were led by Germany, Italy, and Japan. These countries had formed an alliance to expand their territories and exert their dominance over the world.

Allies
The Allies were the countries that fought against the Axis Powers during World War II. The Allies were led by Britain, USSR, USA, and France. These countries had formed an alliance to defend themselves against the aggression of the Axis Powers and to protect the world from their expansionist policies.

Causes of World War II
The causes of World War II were many. The Treaty of Versailles, which ended World War I, imposed heavy penalties on Germany and weakened it as a nation. This led to the rise of Adolf Hitler and the Nazi Party in Germany, which aimed to restore Germany's power and prestige. Hitler's aggressive foreign policy led to the invasion of Poland in 1939, which triggered the onset of World War II.

Course of World War II
World War II was fought on many fronts, with battles taking place in Europe, Africa, Asia, and the Pacific. The war lasted from 1939 to 1945 and resulted in the deaths of millions of people. The Allies emerged victorious, with Germany and Japan being defeated.

Conclusion
World War II was a devastating global conflict that caused immense loss of life and property. It was fought between the Axis Powers (Germany, Italy and Japan) against the Allies (Britain, USSR, USA, France). The causes of the war were many, but the aggressive foreign policy of Germany was one of the primary triggers. The war lasted from 1939 to 1945 and resulted in the defeat of the Axis Powers.