Second world war has 2 different meanings across 2 categories:
a war between the Allies (Australia, Belgium, Bolivia, Brazil, Canada, China, Colombia, Costa Rica, Cuba, Czechoslovakia, Dominican Republic, El Salvador, Ethiopia, France, Greece, Guatemala, Haiti, Honduras, India, Iran, Iraq, Luxembourg, Mexico, Netherlands, New Zealand, Nicaragua, Norway, Panama, Philippines, Poland, South Africa, United Kingdom, United States, USSR, Yugoslavia) and the Axis (Albania, Bulgaria, Finland, Germany, Hungary, Italy, Japan, Rumania, Slovakia, Thailand) from 1939 to 1945