WW2 and the Aftermath

World War II (WWII or WW2), also known as the Second World War, was a global war that lasted from 1939 to 1945, although related conflicts began earlier.
 It involved the vast majority of the world's nations—including all of the great powers—eventually forming two opposing military alliances

The Empire of Japan aimed to dominate Asia and the Pacific and was already at war with the Republic of China in 1937, but the world war is generally said to have begun on 1 September 1939with the invasion of Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom.

The aftermath of World War II was the beginning of a new era. It was defined by the decline of the old great powers and the rise of two superpowers: the Soviet Union (USSR) and the United States of America (US), creating a bipolar world. Allied during World War II, the US and the USSR became competitors on the world stage and engaged in what became known as the Cold War, so called because it never boiled over into open war between the two powers but was focused on espionage, political subversion and proxy wars. Western Europe and Japan were rebuilt through the American Marshall Plan whereas Eastern Europe fell in the Soviet sphere of influence and rejected the plan.

 Internationally, alliances with the two blocs gradually shifted, with some nations trying to stay out of the Cold War through the Non-Aligned Movement. The Cold War also saw a nuclear arms race between the two superpowers; part of the reason that the Cold War never became a war was that the Soviet Union and the United States had nuclear deterrents against each other, leading to a mutually assured destruction standoff.

At the end of the war, millions of people were homeless, the European economy had collapsed, and much of the European industrial infrastructure had been destroyed. The Soviet Union, too, had been heavily affected.As a result of the new borders drawn by the victorious nations, large populations suddenly found themselves in hostile territory.