Anyone who believes that we in the West live in a "surveillance society" today should see The Lives of Others, Florian Henckel von Donnersmarck's film about the Stasi, the East German secret police, or read the screenplay, which has just been published by Pushkin Press (£8.99). The Stasi's penetration of East German society was total: one in seven was an informer and they employed ten times as many agents per capita as the Gestapo had done. Even in Bonn, the West German capital, the Stasi were legion. As a schoolboy living with a German family in 1974, I was shocked to discover that Willy Brandt, the Chancellor, had been forced to resign after his aide Günter Guillaume was unmasked as a Stasi agent. By the time I was working in Bonn as a foreign correspondent in the late 1980s, the Stasi were even more ubiquitous there. The spymaster of the Stasi's foreign intelligence service, Markus ("Mischa") Wolf, later wrote a lively but self-aggrandising memoir, Man Without a Face, with Anne McElvoy. But it is only a slight exaggeration to say that Wolf knew everything that mattered about everybody who mattered in Bonn. The legacy of this is the continuing espionage hysteria in Germany, especially since the revelations of Edward Snowden, who is seen there as a hero rather than a traitor. Berlin's security relationship with Washington is now worse than at any time since 1945.

But the open society that the wartime generation died for and the Cold War generation lived for is now taken for granted. Most people no longer feel any obligation to make sacrifices — of lives, privacy, even money — to defend freedom, democracy and the rule of law. Instead, we retreat into a virtual world where we can treat the forces that in reality threaten our open society as though they too could be deleted at the click of a mouse.

Our leaders aim to defend the West, not by defeating our enemies but by keeping them at arm's length. This new strategy of containment has bought us time, but we shall pay dearly for our unwillingness to give primacy to foreign policy and defence, as we did in the Cold War. Compared to the first two interventions in Iraq, the latest one by the Obama administration seems too little and too late. As I write, Islamic State forces are close enough to Baghdad to shell its international airport. The Pentagon insists that IS does not pose an "imminent threat" to the Iraqi capital, but we must reckon with the possibility of a siege. If IS were to take Baghdad, the reverberations would be felt for decades throughout the world. Not since the fall of Saigon would American — and Western — prestige have suffered such a blow. We just can't let it happen.

Since the fall of the Berlin Wall, the world has become a better place: life, liberty and the pursuit of happiness are now within the grasp of countless millions who could only dream of them before. But any defence of the Western civilisation that has conferred these blessings requires constant vigilance, including reflection on why the ideology that erected the Wall eventually collapsed. Even with the enemy at the gates, the denigrators of the West will not desist. Pankaj Mishra in the Guardian sneers that "Anglo-American elites who are handsomely compensated to live forever in the early 20th century . . . will never cease to find more brutes to exterminate." On the contrary: unless we learn the right lessons of the Cold War, it is the brutes who will exterminate us.