NATO was established in Washington on 4 April 1949. It was a military alliance of capitalist countries from the Northern hemisphere. It relied on the theory of collective security – if one NATO member state was attacked, the other member states would help defend it.
By 1949, Stalin had managed to install communist governments in most Eastern European countries to act as a ‘buffer zone’ to protect the USSR from attack. There was a fear that the USSR could do the same to countries in Western Europe. As part of NATO, smaller countries would be less vulnerable to Soviet influence or attack.
The Berlin Blockade of 1948 convinced the West that they needed a defensive organisation, in the event of a Soviet attack on a capitalist country.
China had become communist in 1949 followed by North Korea in 1950. This significantly increased the proportion of the world which was ‘red’. The USA was concerned that communism would now spread to other countries.
The formation of NATO meant that the USA could place weapons in member states. This would allow more effective defence in the event of a Soviet attack.
In theory, American nuclear missile sites could be established close to the Soviet border. Being part of NATO emphasised to the USSR that the USA was determined to stop communism spreading to the West.