The correct answer is nuclear war.
The Cuban missisle crisis began after the United States discovered that the Soviet Union put missiles in Cuba, which is only 90 miles away from the US. Kennedy feared that the Soviet Union was getting ready to attack the US with these missiles. This began a tense thirteen day negotiation between the US and Soviet Union regarding these missiles.
This was the closest the world has ever come to nuclear war. However, Kenneyd and Khruschev were able to come to an agreement before it got to this point. The Soviet Union would remove their missiles from Cuba. The US would remove their missiles from Turkey and promised never to invade Cuba again.