Who were the primary antagonists during World War 2?

From a purely technical, military and chronological frame, the primary

antagonists were Germany under the Nazi Party led by Adolf Hitler,

Japan under its military (and so-called revival of bushido code) regime, and the Italian Fascist Regime under Benito Mussolini . That would address the

basic antagonists of just before and perhaps during the War. However, if

you ask what actually caused it, then you have to look back to the Treaty of

Versailles of 1918 and the failure of treaty enforcement and the rearmament

of Germany, to start. For the Japan question you would have to look at the

relationship between oil and steel and the U.S.A. and Japan and embargos

in the 30's, and Italian colonialism and domestic turbulence.

Don't forget that it takes "two to tango". Have fun.