The 1940s (pronounced "nineteen-forties" and commonly abbreviated as "the '40s" or "the Forties") was a decade that began on January 1, 1940, and ended on December 31, 1949.

Most of World War II took place in the first half of the decade, which had a profound effect on most countries and people in Europe, Asia, and elsewhere. The consequences of the war lingered well into the second half of the decade, with a war-weary Europe divided between the jostling spheres of influence of the Western world and the Soviet Union, leading to the beginning of the Cold War. To some degree internal and external tensions in the post-war era were managed by new institutions, including the United Nations, the welfare state, and the Bretton Woods system, facilitating the post–World War II economic expansion, which lasted well into the 1970s. The conditions of the post-war world encouraged decolonization and the emergence of new states and governments, with India, Pakistan, Israel, Vietnam, and others declaring independence, although rarely without bloodshed. The decade also witnessed the early beginnings of new technologies (such as computers, nuclear power, and jet propulsion), often first developed in tandem with the war effort, and later adapted and improved upon in the post-war era.

The world population increased from about 2.25 to 2.5 billion over the course of the decade, with about 850 million births and 600 million deaths in total.

Politics and wars

Wars

• World War II (1939–1945)
  • Nazi Germany invades Poland, Denmark, Norway, Benelux, and the French Third Republic from 1939 to 1941.
  • Soviet Union invades Poland, Finland, occupies Latvia, Estonia, Lithuania and Romanian region of Bessarabia from 1939 to 1941.
  • Germany faces the United Kingdom in the Battle of Britain (1940). It was the first major campaign to be fought entirely by air forces, and was the largest and most sustained aerial bombing campaign up until that date.
  • Germany attacks the Soviet Union (June 22, 1941).
  • Continuation War (Second Soviet-Finnish War), was a conflict fought by Finland and Nazi Germany against the Soviet Union from 25 June 1941 – 19 September 1944.
  • The United States enters World War II after the attack on Pearl Harbor on December 7, 1941. It would face the Empire of Japan in the Pacific War.
  • Germany, Italy, and Japan suffer defeats at Stalingrad, El Alamein, and Midway in 1942 and 1943.
  • Warsaw Ghetto Uprising in 1943 was the largest Jewish uprising in Nazi-occupied Poland.
  • Warsaw Uprising against Nazis in 1944 in Poland was the single largest military effort taken by any European resistance movement during World War II.The United States Army Air Forces send support for Poles on September 18, 1944, when flight of 110 B-17s of the 3 division Eighth Air Force airdropped supply for soldiers.
  • Normandy landings.