The Immediate Trigger: Invasion of Poland
World War II began on September 1, 1939, when Nazi Germany, under Adolf Hitler, invaded Poland using a strategy known as Blitzkrieg. This unprovoked attack violated international agreements and prompted Britain and France, who had guaranteed Poland's security, to declare war on Germany two days later on September 3, 1939. The Soviet Union also invaded eastern Poland on September 17 under the secret Molotov-Ribbentrop Pact, dividing the country between the two powers.
Underlying Causes: Post-World War I Tensions
The roots of World War II trace back to the aftermath of World War I, particularly the harsh Treaty of Versailles in 1919, which imposed severe reparations, territorial losses, and military restrictions on Germany. Economic instability during the Great Depression fueled the rise of totalitarian regimes, including Hitler's Nazi Party in Germany, Mussolini's Fascists in Italy, and militarism in Japan. Policies of appeasement by Britain and France, such as allowing Germany's annexation of Austria in 1938 and the Sudetenland via the Munich Agreement, emboldened aggressive expansionism.
Key Events Leading to War: Expansion and Alliances
In 1936, Germany and Japan formed the Axis alliance, followed by Italy's entry in 1937. Germany's remilitarization of the Rhineland in 1936 went unchallenged, and the invasion of Czechoslovakia in 1939 further demonstrated the failure of diplomacy. Japan's invasion of Manchuria in 1931 and China in 1937 escalated global tensions, while the Spanish Civil War (1936-1939) served as a testing ground for German and Italian forces, highlighting the growing threat of fascist powers.
Global Significance and Lessons
The start of World War II marked the beginning of the deadliest conflict in history, involving over 100 million people and resulting in 70-85 million deaths. It reshaped international relations, leading to the formation of the United Nations and the division of the world into Cold War blocs. Understanding these causes underscores the importance of addressing economic grievances, enforcing international law, and avoiding appeasement to prevent future global wars.