In August 1949, the US received shocking news that the USSR had successfully tested an atomic bomb. In reaction, the US began to stockpile nuclear weapons. While in October 1949, the Chinese communist Mao Zedong triumphed over the Chinese nationalists and established a communist state.

The Cold War developed along a number of lines:

Propaganda and distrust
- Neither side would ever trust the other or claim one acted responsibly or morally, seen by negative propaganda
- Each side would bombard their own population with propaganda of the greatness of their cause and the evil nature of the enemy
Alliances
- Form alliances to protect their own security, while claiming opponents alliances were aggressive and a threat
- Help any other state that was opposed to the other side
Nuclear peace and 'proxy' wars
- USSR developed their own atomic bomb in 1949, with such a large scale threat nuclear weapons ensured peace and prevented war between the superpowers
- Both sides engaged in 'proxy wars' - supporting their allies in local conflicts without directly engaging with one another