The USA were concerned that the USSR was building
more powerful nukes than them, the USSR's Tsara
bomb was 1000 times more powerful than the first
atomic bomb
The USSR had feas over how close the USA's missile were
to Russia, in 1961 the USA had put missiles in Turkey it
also has B52 bombers capable of dropping bombs on the
USSR
Both sides were anxious about the other side
gaining the edge
Both sides put huge effort into spying on each other
Cuba became a Soviet ally and Khruchshev was keen to put missiles on the
island which was only 90 miles from florida