What started World War II?

World War II was triggered by a combination of political, economic, and social factors that built up over the years following World War I. One of the key immediate causes was the aggressive expansionist policies of Nazi Germany under Adolf Hitler. After coming to power in 1933, Hitler sought to overturn the Treaty of Versailles, which had imposed heavy penalties on Germany after World War I, and to expand German territory. This led to the remilitarization of the Rhineland in 1936, the annexation of Austria in 1938 (Anschluss), and the occupation of the Sudetenland region of Czechoslovakia following the Munich Agreement. The invasion of Poland by Germany on September 1, 1939, is widely regarded as the official start of World War II. Britain and France had promised to protect Poland’s sovereignty, and in response to the invasion, they declared war on Germany two days later. This act marked the beginning of large-scale conflict in Europe. Other important contributing factors included the failure of the League of Nations to prevent aggression, unresolved issues from World War I, economic instability during the Great Depression, and the rise of militaristic regimes not only in Germany but also in Italy and Japan. These regimes pursued territorial expansion, which destabilized international relations and set the stage for a global conflict.

World War II was triggered by a combination of political, economic, and social factors that developed over the years following World War I. The immediate cause was Germany’s invasion of Poland on September 1, 1939, which led Britain and France to declare war on Germany two days later. However, the roots of the conflict run deeper. After World War I, the Treaty of Versailles in 1919 imposed harsh penalties and territorial losses on Germany, causing widespread resentment and economic hardship. This environment helped extremist political movements, such as Adolf Hitler’s Nazi Party, gain support by promising to restore Germany’s power and pride. Meanwhile, aggressive expansionist policies by totalitarian regimes also contributed to rising tensions. Japan sought to dominate Asia, Italy under Mussolini pursued expansion in Africa, and Germany aimed to overturn the postwar order in Europe. Key events escalating toward war included Germany’s remilitarization of the Rhineland (1936), the annexation of Austria (Anschluss, 1938), and the takeover of the Sudetenland after the Munich Agreement (1938). These actions went largely unchecked by other powers, emboldening Hitler further. The final spark was Germany signing a non-aggression pact with the Soviet Union in August 1939, which cleared the way for the invasion of Poland without fear of a two-front war. Collectively, these developments set the stage for the global conflict that became World War II.

World War II began primarily due to a combination of unresolved issues from World War I, aggressive expansionist policies by totalitarian regimes, and failures in diplomacy during the interwar period. The Treaty of Versailles (1919), which ended World War I, imposed harsh penalties and territorial losses on Germany. This created deep economic hardship and national resentment, especially under the Great Depression, which helped fuel the rise of Adolf Hitler and the Nazi Party, who promised to restore Germany’s power. Key events that directly led to the outbreak of war include Germany’s invasion of Poland on September 1, 1939. Prior to this, Germany had already violated the Treaty of Versailles by remilitarizing the Rhineland (1936), annexing Austria (Anschluss, 1938), and seizing the Sudetenland region of Czechoslovakia (Munich Agreement, 1938). These aggressive moves were met with limited resistance from Britain and France, who followed a policy of appeasement hoping to avoid another large-scale conflict. The invasion of Poland triggered Britain and France to declare war on Germany, marking the official start of World War II. Alongside Germany’s actions, Japan’s expansion in East Asia and Italy’s ambitions in Africa contributed to the global nature of the conflict. Thus, the war arose from a mix of political, economic, and military factors, combined with failures of diplomacy and the rise of militaristic regimes aiming to overturn the post-World War I international order.