When did the axis powers join?

Answer 1

On November 1, 1936, Germany and Italy, reflecting their common interest in destabilizing the European order, announced a Rome-Berlin Axis one week after signing a treaty of friendship. Nearly a month later, on November 25, 1936, Nazi Germany and Imperial Japan signed the so-called Anti-Comintern Pact directed at the Soviet Union. Italy joined the Anti-Comintern Pact on November 6, 1937. On May 22, 1939, Germany and Italy signed the so-called Pact of Steel, formalizing the Axis alliance with military provisions. Finally, on September 27, 1940, Germany, Italy, and Japan signed the Tripartite Pact, which became known as the Axis alliance

Source: http://www.ushmm.org/wlc/en/article.php?ModuleId=10005177