World War II was a global conflict that lasted from 1939 to 1945 and involved the majority of the world's nations, including all of the great powers. It was fought between the Allied powers, consisting of the United States, the United Kingdom, France, and the Soviet Union, and the Axis powers, consisting of Germany, Italy, and Japan. The war was marked by significant events involving the mass death of civilians, including the Holocaust in which approximately 11 million people, including six million Jews, were systematically murdered by the Nazi regime, and the only use of nuclear weapons in warfare.
The causes of World War II can be traced back to the aftermath of World War I and the Treaty of Versailles, which imposed harsh reparations on Germany and stripped it of its overseas colonies and military capabilities. The treaty also created new countries in Eastern Europe, which led to tensions between the newly created states and the neighboring countries that lost territory. The economic downturn following the Great Depression also contributed to the rise of authoritarian regimes in Germany, Italy, and Japan, which sought to expand their territories through military means.
The war began on September 1, 1939, when Germany invaded Poland, and the United Kingdom and France declared war on Germany two days later. The invasion of Poland was followed by a series of campaigns and treaties that saw Germany and the Soviet Union annex territories of their European neighbors, including Finland, the Baltic states, and parts of Romania. In June 1941, Germany turned on the Soviets, opening the Eastern Front, which became the largest and deadliest theatre of the war. The Nazi regime embarked on a campaign of extermination and enslavement, committing genocide against Soviet and Polish Jews and various other groups deemed "unworthy of life" by the regime.
Meanwhile, in the Pacific War, Japan, a member of the Axis powers, launched a series of attacks on Western colonial territories in Southeast Asia and the Pacific, including the bombing of Pearl Harbor in December 1941, which prompted the United States to declare war on Japan. The United States, along with China and several other countries, formed the Allies and defeated the Axis powers in the Pacific War.
The war in Europe concluded with the capture of Berlin by Soviet and Polish forces and the subsequent German unconditional surrender on May 8, 1945. The dropping of atomic bombs on the Japanese cities of Hiroshima and Nagasaki in August 1945 led to Japan's surrender and the end of the war.
The aftermath of World War II saw the rise of communist states in the Eastern Bloc, the decline of Western European colonialism, and the independence of most countries in Asia and Africa, leading to decolonization. The United Nations, formed in the aftermath of the war, became the first international organization to address global issues such as decolonization and the prevention and removal of threats to peace. The war also contributed to the emergence of a new world order, with the Western powers and the Soviet Union playing dominant roles in global affairs.
The war had a significant impact on the civilian population, with millions of people losing their lives or being displaced as a result of the conflict. The Holocaust, in which millions of Jews and other minority groups were systematically murdered by the Nazi regime, is considered one of the darkest moments in human history. The war also led to the displacement of millions of people, as countries were occupied or devastated by fighting. The economic impact of the war was also significant, with many countries experiencing severe disruptions to their economies. The war led to the collapse of the international trading system and the rise of protectionist policies, which had long-lasting effects on the global economy.
The war had a lasting impact on international relations and the global balance of power.