All of these four countries, during the World War II era had two things in common, dictators and expansionist politics.
Germany was led by Hitler, Italy by Mussolini, Japan, by Hirohito, and the Soviet Union by Stalin, all of which are considered as dictators, and also leaders that had expansionist ambitions, and a very big ones.
All of these countries tried to gain as much territory as possible, committing lots of crimes against the humanity in meantime.
Germany was trying to capture all territories that it considered as traditionally German, and also committing genocide in meantime over lots of different ethnic groups.
Italy was trying to restore the Roman Empire.
Japan was invading territories rich in natural resources and that had great strategic positions, making genocide over the Chinese in meantime and raping most of the women in Korea.
Stalin was occupying most of Eastern Europe by using brutal military force.