Timothy Garton Ash: The New Rome is Not the New Greece Yet, But the US Must Look to its laurels

Timothy Garton Ash is a historian, political writer and Guardian columnist. His personal website is www.timothygartonash.com.

We are approaching the anniversary of America's Independence Day. As we all know, 15 years ago an alien invasion, deploying giant saucer-shaped warships hovering over earth, was repulsed by the ingenuity, true grit and heroism of US forces, leading a worldwide coalition of the willing. President Thomas J Whitmore declared that 4 July would henceforward be celebrated as Independence Day not just for the US but for the entire world. His speech was described by one reviewer as "the most jaw-droppingly pompous soliloquy ever delivered in a mainstream Hollywood movie" – which, given the competition, is saying a lot.

It's just a movie, of course, but the 1996 blockbuster is also a document of its time. It returns us to a moment when America seemed to rule supreme, all-powerful, irresistible, in life as in the movies. The new Rome, Prometheus unbound, boasting the mightiest military the world has ever seen: here was the hyperpower at the heart of a unipolar world.

What a difference 15 years make. The mightiest military the world has ever seen has since fought two major wars, in Iraq and Afghanistan. Neither of them can be said to have ended in resounding victories. Iraq, which dominated US debate for so many years, is largely forgotten in the media here. It's history – in the American usage of the phrase.

Afghanistan is not over yet. The suicide attack on the Kabul Intercontinental this week showed how far that country still is from basic security, let alone liberal democracy. But, despite mutterings from his military commanders, Barack Obama has declared that American troops will be pulling out according to his preordained timetable. The US, he says, needs to concentrate on nation-building at home. Most Americans seem to agree. The latest Pew poll has 56% of them saying US troops should be brought home from Afghanistan as soon as possible. A recent blog compares Obama with another leader who pulled out of Afghanistan after a decade of military action so as to concentrate on economic and social reconstruction at home. It describes the US president as "Barack Gorbachev".

Well, hang on. To compare the US in 2011 with the Soviet Union in 1988 is to highlight the huge differences between them. Maybe a comparison with Britain in 1911 would be nearer the mark...