The crisis was caused by the placement of Soviet nuclear weapons in Cuba, an island that was within the US sphere of influence and launching distance. That was arguably an act of brinkmanship by the Soviets to intimidate the US with weapons within the region. The US responded to the presence of the weapons by blockading Cuba. The Cuban blockade was also an act of brinkmanship since the Americans, instead of succumbing to the pressure from the Soviets, decided to see how the Soviets would react to the Americans stopping their vessels from entering Cuba.