How did the Versailles Treaty affect the outbreak of World War II, ie was it a major cause?
The terms of the Treaty of Versailles which were imposed on Germany were unduly harsh; and other nations, notably Japan, were unhappy with other provisions of the Treaty. These provisions of the Treaty were a direct and proximate cause of World War II.
Among the terms imposed upon Germany were the famous War Guilt Clause whereby Germany assumed responsibility for the entire war.
The Allied and Associated Governments affirm and Germany accepts the responsibility of Germany and her allies for causing all the loss and damage to which the Allied and Associated Governments and their nationals have been subjected as a consequence of the war imposed upon them by the aggression of Germany and her allies.
This was of course a fabrication and caused intense resentment among the German people. Further, Germany was required to pay exorbitant reparations to the Allied Powers, and its armed forces dramatically limited. This also caused intense resentment. Finally, a portion of German territory in East Prussia was ceded to Poland in order to give that country access to the sea, even though the people of that area were culturally and ethnically German. These missteps and miscalculations provided a platform for Adolf Hitler who in many speeches taxed the provisions of the Treaty with responsibility for Germany's problems. Had Germany been treated less harshly, it is unlikely that Hitler would have so easily gained the hearing of the German people.
Also, Japan had entered World War I on the allied side, hoping to gain German territory in Asia. In the end, Japan left Paris empty handed. This also created resentment, which played into the hands of the Japanese War Party who soon gained control of the government and began a military expansion into the Pacific Basin. That expansion ultimately led to conflict with the United States and the bombing of Pearl Harbor.