Twenty years ago, great hopes and great fears swept over the continent of Europe and indeed the wider world. Optimism at the possibility of liberation leapt in the hearts of tens of millions living behind the Iron Curtain. But as Berliners tore down the barrier that had separated them for decades, there were also significant concerns about what would emerge from the rubble.
Would the Soviet Union respond by sending in the tanks? Would there be a tidal wave of refugees from east Germany? There were concerns too of a new German dominance of Europe. We have recently learned that Margaret Thatcher even went as far as to lobby Mikhail Gorbachev, the Soviet leader, to prevent reunification.
The alarm of Mrs Thatcher and others fed into a larger sense of uncertainty over what might emerge from this bloodless revolution. As this newspaper put in a leading article at the time, "euphoria and trepidation mingle ... nobody knows what reefs may lie concealed beneath the new ocean we are entering".
Two decades on, we might look back and wonder: which emotion was more justified, euphoria or trepidation? And how successfully did we navigate those hidden reefs? Russia, of course, let her European empire expire without a shot being fired. And we can say that the fears about the consequences of a united Germany for Europe have not been realised.
A unified Germany has entrenched its position as a dominant continental power, but it is hardly a malign one. This anti-militaristic democracy is a pillar of the single market and the European Union.
The broad hopes of 1989, on the other hand, have been amply fulfilled. The fall of the Berlin Wall led not only to freedom for eastern and central Europeans, but the collapse of the Soviet Union itself. The end of the Cold War meant that the threat of nuclear annihilation considerably receded. Economic and social progress has flowed from liberation. Eight former Soviet Bloc nations have even joined the European Union. Others aspire to.
The revolution of 1989 helped to kick off a new era of economic advance around the globe. Lately we have suffered a significant setback on that front with the banking crisis and global economic downturn. But that cannot overshadow just how far we have come in setting free the economic potential of the world's population.
But, of course, history is never a bloodless process. Even great advances for humankind such as the end of the Soviet Union tend to have terrible side effects. Brutal ethnic wars broke out in the Balkans as the former communist state of Yugoslavia fragmented. Russia sank into a chaos of free-market gangsterism, a brutal experience which sowed the seeds for its present retreat into authoritarianism.
Further afield, China embraced the market economy, but not democracy. The defining moment for the Chinese people in 1989 was not the fall of the Berlin wall, but the slaughter in Tiananmen Square.
The euphoria of that moment twenty years ago has been vindicated. Few would seek to rebuild that wall. But we cannot afford more than a brief moment of satisfaction. Challenges crowd the scene: climate change, Islamist terrorism, economic dislocation, nuclear proliferation. The world managed to pull one wall down. But many remain.