The Second World War, which raged from 1939 to 1945, was a conflict that was between two major coalitions of countries. One of the sides was the Allies, consisting of Great Britain, the United States of America, France and the Soviet Union. While there were others, those were the major players on the side of the Allies. The other side, however was called the Axis Powers.
The Axis Powers consisted of three major early 20th century powers. The first was Germany, led by Adolf Hitler. The second was Italy, led by Benito Mussolini. The final member of the Axis powers was Japan, led by the Emperor Hirohito. Like the Allies, there were other members of the Axis powers, however, Japan, Italy and Germany were the major members.
The Axis powers began as a preliminary alliance between Germany and Italy in 1936. The two powers sought to make the world rotate on a new axis, one that ran through Berlin and Rome, the respective capitals of Germany and Italy. The declaration of a new "Axis" for the world is what gave this faction its name.
Soon after the declaration of this new world axis, Germany began to look for other allies in order to oppose Joseph Stalin and the Soviet Union. To this end, Germany signed the Anti-ComIntern Pact with the Empire of Japan in 1936. One year later, Italy joined the Anti-ComIntern Pact in order to further their ties with Germany and Japan and to further oppose the Soviet Union.
In 1939, the Pact of Steel, between Germany and Italy brought a military aspect to what was before an alliance on paper, making it a formal military alliance. Finally, one year after the signing of the Pact of Steel, in 1940, Germany, Japan and Italy signed the Tripartite pact. This pact began the formal alliance of the three nations that is known today as the Axis powers. This formal alliance only served to fuel the flames of World War Two, escalating what would become one of the most costly wars in human history.