The main cause behind the international conflicts following World War I was the dissatisfaction stemming from the Treaty of Versailles, which imposed harsh penalties and reparations on Germany. This treaty created an environment of resentment and instability, leading to economic difficulties in Germany and fostering extremist political movements, including the rise of Adolf Hitler and the Nazi Party. Nationalist sentiments surged in various regions as newly drawn borders created ethnic tensions, particularly in Eastern Europe and the Balkans. These unresolved issues contributed to the outbreak of World War II in 1939, as countries grappled with the geopolitical realities instituted by the post-war settlement.