What was the main factor for world war 2?

The main factor for World War II was the aggressive expansionist policies of Nazi Germany, led by Adolf Hitler, which aimed to overturn the post-World War I settlement and establish German dominance in Europe. This expansion was fueled by economic instability, nationalistic fervor, and a desire for Lebensraum (living space). The failure of appeasement strategies by Britain and France, combined with the signing of the Molotov-Ribbentrop Pact between Germany and the Soviet Union, further escalated tensions and ultimately led to the outbreak of war in 1939.