World War 2
World War 2 was a global war about 20 years after World War 1.
Axis
The Axis alliance was initially negotiated around the Anti-Comintern Pact, of which the original signatories were Germany and Japan in 1936. Italy joined the next year on condition it was recognized as an original signatory. Hungary and Spain also joined in 1939.
The Molotov-Ribbentrop Pact significantly shifted the balance of power. The Tripartite Pact became the new foundational treaty in 1940. Once again Germany, Italy, and Japan were the original signatories. Hungary and Romania quickly joined. Bulgaria and Yugoslavia joined the following year, though signing led to a coup in the latter, so Yugoslavia was invaded by the other signatories and partitioned between them.
Pacific Theater
China
Western Theater
Czechoslovakia
Albania