On April 26, 1986, a test at the Chernobyl nuclear plant went badly wrong. An explosion occurred and a massive amount of radiation was released into the atmosphere.
The initial Soviet response was first to deny that there had been any problems at the plant, and then to insist that Soviet nuclear engineers were in complete control of the situation.
Had the reactor been located further from the Soviet borders with the West and had the radiation plume not passed over Scandinavia, the Soviet government might have been able to get away with such denials just as Moscow often had succeeded in doing with earlier disasters.
But once Swedish scientists monitored the radiation cloud, radio and television stations in Eastern Europe and Western Europe began to report that an accident had taken place.
And many Soviet citizens learned what had in fact happened, some from cross-border Polish television broadcasts and others from international radio broadcasters.
Mikhail Gorbachev, who had become general secretary of the Communist Party of the Soviet Union only 13 months earlier, was faced with a crisis. If he followed the standard Soviet protocol on such matters, he would not only lose face at home and abroad as a reformer but also risk losing his power base within the Soviet leadership.
Confronted with this choice, Gorbachev first equivocated and then signaled that he was willing to allow the Soviet media to report more accurately on what had happened.
Soviet newspapers, radio stations and television networks began to tell Ukrainians, Russians and Belorusians more of the story, and Gorbachev sought to use this new openness, which he eventually labeled "glasnost," as a means to win popular support and defeat his political enemies.
For the first time, Soviet citizens were hearing more or less accurate information about a disaster in their country not just from foreign radio "voices" but also from their own media. That did not lessen their fears about the consequences of the Chernobyl accident, but it did mean that they now looked to their domestic media as a source of news.
Gorbachev's own hesitations and statements then and later make it clear that he did not recognize what he had begun or where it would lead. Once the Soviet media implicitly and in some cases explicitly acknowledged that Soviet outlets had not told the truth about Chernobyl and nuclear power, Soviet citizens and a growing number of Soviet journalists began demanding a fuller accounting on other issues as well.
Over the next five years, this process accelerated, forcing Gorbachev and the Soviet government to confront ever more controversial questions about the rule of the Communist Party and Soviet nationality policies.
And as Soviet claims were shown to be hollow and false, ever more citizens of the U.S.S.R. turned away not only from the system as a whole but from Gorbachev, who had allowed these revelations to occur.
That shift contributed to the collapse of communism, the demise of the Soviet Union, and the difficult period of transition away from a totalitarian system toward democracy and freedom.
The Chernobyl accident in the first instance called attention to the incredible dangers inherent in the use of atomic power, and many people in Ukraine, Belarus and Russia are still suffering from exposure to radiation.
But at the same time, the aftermath of that accident highlighted the incredible power of a more open press to change people's minds and ultimately to change the course of history.