any conflict between the superpowers had the potential to become a nuclear war.
The correct answer is: "Because it happened during the Cold War, and the world feared a nuclear war".
The Cold War Era (after WWII and during the second half of the 20th century) was a period or direct rivalry exercised by the US and the URSS against each other, although none of them never dared to undertake a direct attack because both superpowers (and the whole world) feared a nuclear war. They never fought directly but, the two of them, usually got involved in opposite sides in proxy wars such as the Korean War or the Vietnam War.
The Cuban Missile Crisis in 1962 was one of the moments in which the tension between the two superpowers was at the highest point. The US discovered that the URSS has sent missiles to be kept in the territority of its ally, Cuba (that was actually a US enemy too). From Cuba, those missiles could actually reach US soil and this strategical movement undertaken by the URSS was regarded by the US as a direct threat.
