The Cold War ended not with a bang but with a picnic.

On August 19, 1989, Miklós Németh, the Hungarian prime minister, opened his nation's border with Austria – for a few hours, he thought.

The supposed "pan-European picnic" at Sopron, Hungary, that afternoon led to the exodus of hundreds of East Germans into Austria and thus into the free West.

When Soviet troops stationed in Hungary did not deploy to prevent this – as Németh feared they might – the Cold War was over.

Within three months the Berlin Wall had fallen; within fourteen months the two Germanys were reunited; within three years of the picnic, the Soviet Union itself ceased to exist.

Since that afternoon in 1989, the world has resisted easy labelling.

Most of the twentieth century can be neatly parcelled into distinct eras: World War I, the interwar years, the Great Depression, World War II, the nuclear era, the Cold War.

Labels provide a reassuring terrain for students of history; compartmentalising the world is often a necessary first step to comprehending it.

At the end of the Cold War, however, the labels for what came next became more various but less reliable. Despite efforts to craft a "new world order" after the formal collapse of America's great enemy, the Soviet Union, in December 1991, no label describing that order has stuck.

We still define the era in which we live now against the era that preceded it: the post–Cold War world.

This might seem like a subject for mere academic debate. But it also lends credibility to the thesis that because the world entered a new era of complexity, the tools of American power, supposedly more successful in simpler times, have been inadequate to meet it.

Whereas the great wars of the last century were decisively turned by the intervention of the United States, since the end of the Cold War, American interventions – military, economic, or diplomatic – have had, according to several accounts, rather more mixed impacts.

Increasing global complexities make foreign policy more difficult.

This, according to the argument, goes some way to explaining the patchy performance of US presidents in foreign affairs for over three decades. None seemed to grasp that the world had shifted.

Each devised a label for the world he inherited; none succeeded in making it permanent.

The most obvious example is the War on Terror.

Invented by President George W. Bush in response to an event of unambiguous clarity even if of disputed meaning – the terrorist attacks of September 11, 2001 – the label itself has never commanded a consensus: "too reductive … war cannot be made on a tactic … too easily construed as a war on Islam … paints a grey world in black and white…".

President Barack Obama never spoke of a War on Terror even as he continued to wage it, killing more terrorists than his predecessor.

Thus, we find ourselves in a distinct historical moment, the parameters of which are fluid and disputed. How did America cope with such a world?

The short answer is "not badly."

My argument is neither a paean to American greatness nor to the perfection of its foreign policy.

Two decades after the Cold War ended, American capitalism looked far from triumphant, as the Great Recession, which took hold in 2008, was evidence. And yet, potentially disastrous as these and other episodes were, the United States remained the world's preeminent power, indebted, certainly, but still preeminent and indispensable.

This is more because of American foreign policy than despite it.

This claim does not mean making a blanket defense of US power in the modern era. But an accounting that recognises its durability, elasticity, and popularity – not its infallibility – is missing from the popular narratives about post-1989 America.

The Cold War cast a shadow on the presidents that came after it.

They did not always have to be aware of operating within that shadow – indeed, several claimed to have moved beyond it – but it nevertheless conditioned how they made foreign policy the way they did, and why.

Success came more from adapting to that shadow than from attempts to escape it. When the strategic lessons of the Cold War were applied, presidents fared better. When they were forgotten, they fared worse.

Despite the initial rhetoric of George H. W. Bush, president at the end of the Cold War, his foreign policy ultimately failed to transcend that conflict.

Similarly, Bill Clinton's efforts to abandon what he called the "old think" of the Cold War were short-lived. He came to rely on Cold War strategies – like containment, in the case of Iraq, and institutions like North Atlantic Treaty Organization (NATO) – to craft his foreign policy legacy.

George W. Bush, despite the drama of 9/11, waged a War on Terror with powerful analogies to the war on communism. Barack Obama, born in 1961, matured personally and politically, like his successor, in a world divided along Cold War lines.

Donald Trump, like so many presidents before him, made Russia central to his foreign policy and was determined to contain Chinese power.

It would be remarkable were these leaders, nurtured in the Cold War, not susceptible to its strategic lessons. It is more remarkable still to suppose that the foreign policy establishment and personnel of the American government could as quickly forget them.

While the world was in many ways different after the collapse of the Soviet Union, the response of the United States to this "new world order" – for both good and ill – was essentially unaltered.

To understand US foreign policy after the Cold War, our essential lens is the Cold War itself.

This theme of continuity is complemented by a second, which argues that, given the challenges facing it after the Cold War, US foreign policy was not a study in failure.

Rather, during this period, American power grew; its supposed challengers did not emerge; states like China and India wanted to be on the American side; despite its enormous power and purported arrogance, the United States earned very few enemies in the post–Cold War years. Russia, its Cold War opponent, was unable to secure many new friends; dictators anathema to US interests and values were toppled; European allies preferred an engaged America to a detached one.

Such successes are owed to the adaptation, not abandonment, of Cold War thinking in this supposedly new world.

This is an edited extract from Associate Professor Tim Lynch's new book In the Shadow of the Cold War published by Cambridge University Press. It's available now online or wherever books are sold.

Banner: Cover art of In the Shadow of the Cold War by Peter Lorenz