I believe that it is any independent nation that signed the tripartite pact and spent most of the war on the side of the Axis. Nations like Yugoslavia do not count since they were invaded by Germany, Italy, and Bulgaria months after signing the Tripartite Pact. Slovakia and Croatia were puppet states created by Germany. Also, Finland, Thailand, and Iraq never signed the Tripartite Pact.
In short, Germany, Italy, Japan, Hungary, Romania, and Bulgaria can be listed as true Axis nations.





