Cold War refers to the intense rivalry that developed after World War II (1939-1945) between groups of Communist led by Union of Soviet Socialist Republics (U.S.S.R.), and non-Communist nations led by USA. It is called cold war because though it involved intense power struggle, as exists in war, but no physical fighting took place. The cold war happened because of the attempts of the USSR to forcibly extend communist rule to other countries. This was opposed by the USA and its allies on grounds of ideological opposition to communism as well as fear of dominance of the world by USSR.

The cold war tension started immediately after end of World War II with USSR acting against some of the agreements reached between the allied countries regarding treatment of Germany and other countries in Eastern Europe freed from German control. At the Yalta conference held in 1945. the USA, UK and the USSR leaders had agreed to hold democratic elections in the liberated countries. However, Stalin refused to honour these commitment after the end of war. He cut off nearly all contacts between the West and the territories it controlled in Eastern Europe, and began to take action to install communist Governments there. As a result, by 1948, Bulgaria, Romania, Hungary, Poland, Czechoslovakia, Albania, and Yugoslavia all had Communist governments. In response USA decided to actively oppose spread of communism. USA adopted a policy in March 1947 to help any free nation resist Communist attack.

In 1949 the Countries on side of USA formed the North Atlantic Treaty Organization (NATO) to Oppose USSR. Similarly in1949, the USSR set up the Council for Mutual Economic Assistance (COMECON) to unite the Communist-ruled states.

The two warring groups also had differences over question of developing and stocking nuclear weapons. They engaged in kind of a race to develop nuclear and other military capabilities. There was similar race in the field of space exploration also. All this further increased the mutual distrust and fear between the two warring groups.

The victory of communists in China in 1949 further added to the fear of communism among USA and its allies. Though there were no direct wars between USA and USSR, there were wars in different countries supported by the opposing groups of the cold war. This includes wars in countries Korea, Vietnam and Afghanistan.

However, by about 1970's the futility of the the Cold war was becoming clearer to both the sides. Also there were some disunity within each group. A a result some initiatives for reducing the cold war tension were taken. As a result the agreement over status of Berlin was reached in 1972 and Germany joined the United Nations in 1973. A Strategic Arms Limitation Talks (SALT) agreement was reached between the USA and the USSR was reached in 1972. China and the USA established diplomatic relations in 1979. We can say the cold war finally came to an end in 1991 with the Soviet Communist party loosing control of the Soviet government and the USSR breaking up into a number of independent, non-Communist states.