In 1983, Soviet satellites had detected a barrage of American missiles coming their way. The man in charge at the time was named Stanislav Petrov. Petrov had orders; if the radars detect an American attack, call for immediate nuclear retaliation. Fortunately, Petrov decided to disobey his instructions. He decided that it was too risky to call for a retaliatory strike until he could confidently confirm the American attack. Petrov reasoned that it was unlikely that America would start world war 3 with a small surprise attack, so that there could be some sort of error. What Petrov did not know at the time was that the KGB did believe at the time the Americans were planning on launching a small surprise attack against them. Had this been passed on to Petrov, he probably would not have waited the extra 10 minutes to see if the attack were real before he called for retaliation (giving the Soviets just enough time to respond). With only moments before Petrov had to call for a response, the missiles disappeared from the radar. Turns out the Soviet satellite had a huge design flaw and there were never any missiles, but merely just high altitude clouds.
On October 16th, 1962, the Americans received satellite footage that Cuba was secretly building launching pads for Soviet missiles that if equipped with nuclear payloads would be able to crush the entire eastern United States, potentially killing 90 million Americans. This was too much of a risk for the Americans to handle and they decided that these sites must be destroyed before they were loaded with nuclear weapons. John F. Kennedy asked his team to prepare a plan to destroy the missiles, and shortly thereafter, a plan was put in place to launch 1080 sorties against Cuba, completely annihilating everything in the vicinity. On Monday, October 29th, the attacks were to start, following an invasion of Cuba a week later.
On Saturday the 27th, two days before the planned attack, an American plane was shot down over Cuba and as things seemed more and more out of control and closer to the brink of war, a former ambassador to the Soviet Union, Llewellyn Thompson, one of the lowest possible ranked members of EXCOMM convinced president Kennedy to wait out the attack, and surprisingly he did. What the Americans didn’t know at the time was that the Cuban missiles were already loaded with nuclear weapons; 162 of them in total. Years later Fidel Castro was asked what would have happened if the Americans launched an attack and this was his response: “Now, we started from the assumption that if there was an invasion of Cuba, nuclear war would erupt. We were certain of that … we would be forced to pay the price, that we would disappear…. Would I have been ready to use nuclear weapons? Yes, I would have agreed to the use of nuclear weapons.…”.
At the very same time this was all going on, there was a Soviet submarine loaded with nuclear weapons that had been submerged underground without radio contact for a few days. They were the target of American shots (which were actually supposed to be warning shots asking the ship to identify itself). Because they could not radio back to Moscow due to the depth of their submersion, the captain of the ship believing that world war 3 must have already started decided to launch the subs nuclear payload at America as instructed. Outnumbered 2-1, the 2nd in command, Vasili Arkhipov, would not let the launch proceed (all three of them needed to authorize it) and made them rise to service and radio back to Moscow.
In 1961, an American airplane accidentally dropped two nuclear weapons (with a payload of more than 250 times greater than Hiroshima’s bomb) into North Carolina. On the way to the ground, 3/4 failsafe’s miraculously launched into place, putting one of the bombs on the verge of explosion. The only thing that prevented it from going off was the physical on/off switch that had not been impacted in the collision with the ground.
There are many stories like this. With a sample size of one, anything can happen. The fact that a nuclear holocaust did not occur during the Cold War is simply luck.