The keywords here are unadulterated aggression, quest for power, and ethnic prejudices. The Axis powers, Germany, Italy, and Japan were known to be aggressive towards countries whom they considered to be "inferior" and "weaker." Japan invaded Manchuria in the 1930s in a bid for more territory. Germany annexed Austria whom it considered to be a fellow German country. It then invaded Czechoslovakia on the pretext of there being a large German population there.
Poland was invaded on the subferfuge of the "indication' by some spies planted by the Nazi government(the Gleiwitz experiment) that the German population in Poland was being mistreated by the Poles. The German invasion of Poland on September 1, 1939 began World War II in the European Theatre. The Japanese under Tojo, a military warload, wanted Japan to establish her miliary hegemony. The Japanese wanted to assauge the Americans that they wanted peace although their ulterior motive was war and conquest. This was proven on December 7, 1941 in the morning hours when the Japanese bombed Pearl Harbor, an military base in Hawaii. That started World War II in the Pacific Theatre.