An arms race is defined as a race between two parties to better each other in military strength. USA and USSR had a very competetive arms race during their cold war, probably anticipating the outbreak of World War III.
In 1952, USA developed and successfully tested the Hydrogen bomb(H-bomb). But the technological advantage lasted only for a year, as in 1953 USSR came up with their own H-bomb. The two superpowers just could not stop trying to get better than the other.
The probability of nuclear wars happening was very real at this stage as the biggest of rivals both had access to nuclear weapons, and relationship between them just continued to get worse, increasing the likelihood that one of them would be tempted to push that button.
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Sources:
http://en.wikipedia.org/wiki/Arms_race
http://en.wikipedia.org/wiki/Nuclear_arms_race
http://en.wikipedia.org/wiki/History_of_nuclear_weapons
http://faatih.wordpress.com/
http://www.atomicarchive.com/History/hbomb/page_09.shtml
http://www.youtube.com/watch?v=fWoNDxjOksM
http://www.youtube.com/watch?v=Bi0WMV7OPyQ
http://www.youtube.com/watch?v=NNcQX033V_M
http://www.youtube.com/watch?v=r3l0G3XOUv4
http://upload.wikimedia.org/wikipedia/commons/3/3d/IvyMike2.jpg
History Notes.
