The cold war was an intense and prolonged period of confrontation between the Soviet Union and the United States. The two nations were allies during World War II in order to defeat Nazi Germany and its allies. ASt the end of the war in Europe, the Soviet Union was allowed to occupy most of eastern Europe. Germany itself was divided into four zones of occupation. The three western allies (UK, US and France) took charge of the western zones while the USSR took the remaining territory in northeast Germany. The city of Berlin, although located deep within the Soviet zone, was also divided into four zones. The Soviets maintained control of only the eastern part of the city. Although an earlier plan provided for the establishment of a government for a unified Germany, political and ideological differences between the west and the Soviet Union made this outcome increasingly unlikely as time went on.
In the early years of the war, the Soviets had invaded and annexed the Baltic republics, Latvia, Lithuania and Estonia. In the first couple of years after Germany's surrender, the USSR forced Communist governments upon Poland, Bulgaria, Romania and other eastern European nations. In 1948, the Soviets withdrew from the Allied Control Council and declared their zone to be a separate nation, the German Democratic Republic (DDR) the following year.
In June 1948, the Soviet Union blocked road and rail access from West Germany to West Berlin. This was an attempt to keep West Germany from introducing the West Germany mark, a stable currency, from West Berlin. It was also seen as an attempt to allow the East German government and the Soviet Union to attain greater influence and control over the entire city of Berlin. In response, the western nations organized a massive airlift operation to supply the city. Over the next year, more than two million tons of supplies were flown into the city. Unaable to achieve their goals, the Soviets lifted the blockade on 12 May 1949.
After the war, open conflict between the Nationalist Chinese goverment led by Chiang Kai-Shek and Communist forces under Mao Zedong resumed. The two forces had forged an uneasy alliance in the 1930s to resist the Japanese expansion into China. The Communists entered the renewed civil war with the advantage of widespread popular support, better military organization and a large stockpile of weapons seized from the Japanese in Manchuria. On 1 October 1949, Mao declared the establishment of the People's Republic of China. Shortly, the defeated Nationalist leaders and remaining armed forces left the mainland and re-established their government on the island of Taiwan, where it remains.
Competition between the United States and the Soviet Union soon developed along a number of fronts. One of these was the so-called nuclear arms race. The US was the world's sole nuclear power until August 1949, when the USSR tested its first atomic weapon, RDS-1, dubbed "Joe 1" by the Americans. This achievment led to a frenzy of activity by both nations to develop not only bigger and more powerful weapons but also bigger and more powerful missiles to carry those weapons to their destinations. Within a few years, both sides possessed enough of these weapons to ensure that should one side initiate an attack, the resulting counter attack would ensure that both sides would be destroyed and possibly bring about the extinction of life on earth.
In the 1950s, the prospect of nuclear war led to the development of civil defense plans and the designation of public shelters in the basements of schools and other public buildings. Films, such as "Duck and Cover", were produced to instruct citizens about what to do in the event of an attack. School children were told to take shelter under their desks or in hallways, although these actions would be of little value in the event of an actual attack. Many people built bomb shelters in their basements or backyards and stockpiled food and water. In many communitites, air raid sirens were tested on a weekly basis.
The next hot spot of the Cold War flared up in Korea. That nation had been ruled by Japan since 1910. The Soviet Union didn't join in the Pacific war until it declared war on Japan on 8 August 1945, a couple of days after the bombing of Hiroshima. Almost immediately, Soviet troops began to occupy the northern regions of Korea. After the Japanese surrender, Korea was divided into two zones of occupation, the Soviets in the north and the Americans in the south.
Joint administration of Korea as a whole lasted for about three years. For a while, it was planned to hold elections to establish a government for a unified Korea. However, differences between the USSR and the US soon made that improbable. In 1948, the peninsula was divided along the 38th parallel, the border between the two zones. A communist government was installed in the Soviet zone (Democratic People's Republic of Korea) while a US friendly regime was established in the south (Republic of Korea).
For the next two years, communist instigated insurgency and guerrilla warfare rocked South Korea. North Korea aimed to destabilize and ultimately cause the downfall of the non-communist forces in South Korea, which would pave the way for unification under a communist government. On 25 June 1950, North Korean forces invaded the south. Encouraged by US President Harry S Truman, the United States succeeded in convincing the United Nations Security Council to come to the aid of South Korea with an international force. However, the situation looked bleak at first. Within a short time, forces of the Korean People's Army had forced the UN troops into a very small area in the southeast region of the peninsula. In September, the tide changed and the UN troops were able to break out and pursue the communist forces northward. By the following month, the UN forces had taken almost all of North Korea and it looked as though the war would soon come to an end. However, China entered the conflict, sending close to a million troops across the border into Korea. The United States and allies were soon pushed back to the 38th parallel, where the war remained for the next two years in a bloody stalemate. On 27 July 1953, the warring parties signed an armistice, which led to a continuation of a divided Korea with no formal peace treaty, a situation that remains today.