06 The Second World War and Its Aftermath

Origins and outbreak

The Second World War was a global conflict fought from 1939 to 1945 across Europe, Africa, Asia, and the oceans. It grew from aggressive expansion by authoritarian states and the failure of international efforts to prevent war.

Its causes included the unsettled legacy of the First World War. The Treaty of Versailles and the economic and political crises that followed contributed to instability in Germany. The Great Depression further weakened confidence in democratic governments and helped extremist movements gain support. Nazi Germany, Fascist Italy, and militarist Japan pursued expansion by force, while the League of Nations proved unable to stop aggression.

The conflict developed at different times in different regions. Japan occupied Manchuria in 1931 and launched a full-scale invasion of China in 1937. Germany annexed Austria in 1938 and occupied the rest of Czechoslovakia in March 1939. Germany invaded Poland on September 1, 1939, and Britain and France declared war two days later. Germany and the Soviet Union had secretly agreed to divide parts of Eastern Europe; Soviet forces invaded eastern Poland later that month.

The war became fully global in December 1941, when Japan attacked Pearl Harbor and other Allied positions in the Pacific. The attack prompted the United States to enter the war, after which Germany and Italy declared war on the United States.

Europe and the Eastern Front

Germany quickly occupied much of Western Europe in 1940, but Britain remained at war after the Battle of Britain prevented a German invasion. In June 1941, Germany invaded the Soviet Union, opening the vast and exceptionally deadly Eastern Front. The invasion was also a war of racial conquest: Nazi forces and collaborators committed mass murder, including the Holocaust, in which six million Jews were killed, alongside the persecution and murder of millions of other victims.

The German advance into the Soviet Union failed to achieve a quick victory. The German defeat at Stalingrad in 1942–1943 marked a major shift, as Soviet forces began pushing west. The Soviet victory at Kursk in 1943 further weakened Germany’s ability to regain the initiative.

In June 1944, the Allied landing in Normandy opened a major western front. Allied forces advanced through France while Soviet armies drove into Eastern Europe and Germany. Germany surrendered in May 1945.

North Africa and the Atlantic

Control of North Africa and the Mediterranean mattered for access to shipping routes and the Suez Canal. British forces halted Axis advances at El Alamein in 1942, while US and British troops landed in French North Africa. Axis forces in the region surrendered in 1943, allowing the Allies to invade Sicily and then Italy.

In the Battle of the Atlantic, German submarines sought to disrupt the supply lines linking North America and Britain. Allied convoy systems, new technologies, and improved coordination gradually reduced the submarine threat. This helped sustain the buildup for the liberation of Western Europe.

Asia and the Pacific

After Pearl Harbor, Japan rapidly seized territory across Southeast Asia and the Pacific. The United States and its allies halted Japanese expansion at the Battle of Midway in June 1942, a major naval turning point. The campaign for Guadalcanal and subsequent advances across the Pacific gradually brought Allied forces closer to Japan. China remained a major battlefield throughout the conflict, fighting Japanese occupation with enormous civilian and military losses.

In 1945, US forces captured Okinawa, while Allied bombing devastated Japanese cities. The United States dropped atomic bombs on Hiroshima on August 6 and Nagasaki on August 9. The Soviet Union entered the war against Japan on August 8 and invaded Japanese-held Manchuria. Japan announced its acceptance of surrender terms in August and formally surrendered on September 2, 1945.

Global consequences

The war caused immense military and civilian loss, mass displacement, and destruction across several continents. The Holocaust—the systematic genocide of European Jews by Nazi Germany—was central to the history of the conflict; other groups were also targeted for persecution and mass murder. The use of atomic weapons introduced a new era in which warfare could threaten destruction on an unprecedented scale.

The war weakened European empires and strengthened independence movements. Japan’s wartime defeat of European colonial powers in parts of Asia had undermined their authority. After 1945, nationalist movements pressed to prevent the return of colonial rule. Decolonization unfolded unevenly through both negotiation and armed struggle, creating dozens of independent states in Asia and Africa. Many of these states had to navigate the emerging rivalry between the United States and the Soviet Union.

The United States and the Soviet Union emerged as the most powerful states. Their competing political and economic systems shaped the Cold War, which influenced international politics for decades. In 1945, countries founded the United Nations, seeking a forum for cooperation and a means to prevent another world war. Postwar reconstruction, trials of some war criminals, and the development of new institutions reflected efforts to address the conflict’s devastation and establish a different international order.

Course and outcome

World War II grew from expansionist ambitions, political instability, and the failure to stop aggression. It became a global struggle in which the Allies gained the initiative through turning points including Stalingrad, El Alamein, Midway, and the Normandy landings. The war ended with Germany’s surrender in May 1945 and Japan’s surrender in September.

Its consequences included the Holocaust, atomic warfare, the rise of the United States and Soviet Union as the most powerful states, the creation of the United Nations, and the acceleration of decolonization.