It is hard to imagine a period since the end of the Cold War when relations between Russia and the United States have been quite so bad.

US officials have described the joint Russian-Syrian onslaught against Aleppo as "barbarism" and warned that war crimes are being carried out.

The Russian president has spoken explicitly about the worsening climate between Washington and Moscow, insisting that what the Obama administration wants is "diktat" rather than dialogue.

For all that, the US and Russia are still in contact over Syria. For all the harsh rhetoric and accusations, they both realise that they have a vital role to play in any eventual settlement of the Syrian drama.

Whatever its immediate strategic intentions, a permanent war in Syria doesn't benefit Moscow any more than Washington.

But without that basic level of trust and understanding between them, any dialogue rests upon shaky foundations. It was never supposed to be like this. The end of the Cold War was supposed to usher in a new era.

For a time Russia retreated from the world stage, but now it is back with a vengeance, eager to consolidate its position nearer home; to restore something of its former global role and to make up for perceived slights perpetrated by the West.

So where did it all go wrong? Why were Russia and the West unable to forge a different type of relationship? Who is to blame? Was it US over-reach and insensitivity, or Russia's nostalgia for Soviet greatness? Why have things now got so bad and is it correct to describe the present state of affairs as a "new Cold War"?

I am not going to try to give a comprehensive answer to all these questions - the intricacies of this story would require a book the length of Tolstoy's War and Peace! But I am going to try to throw out some pointers.

For Paul R Pillar, a senior fellow at the Centre for Security Studies at Georgetown University and a former senior CIA officer, the initial fault lies with the West.

"The relationship went wrong when the West did not treat Russia as a nation that had shaken off Soviet Communism," he told me. "It should have been welcomed as such into a new community of nations - but instead it was regarded as the successor state of the USSR, inheriting its status as the principal focus of Western distrust."

This original sin, if you like, was compounded by the West's enthusiasm for Nato expansion, first taking in countries like Poland, the Czech Republic and Hungary, who had long nationalist traditions of struggling against rule from Moscow.

But Nato's expansion didn't end there as it added countries like the three Baltic States, whose territory had been part of the former Soviet Union. Is it any wonder then, the critics ask, that Moscow should baulk also at the idea of Georgia or Ukraine entering the western orbit?

In short, Russia believes that it has been treated unfairly since the end of the Cold War.

This, of course, is not the conventional view in the West, which prefers to focus on Russian "revanchism" - a stance personified by Vladimir Putin, a man who has described the collapse of the Soviet Union as "the greatest geopolitical catastrophe" of the 20th century.

There is an interesting debate going on among US think tank experts as to which camp is right. Should one focus on the initial strategic errors of the West in dealing with the new Russia, or look at Moscow's more recent assertive behaviour in Georgia, Syria or Ukraine?

Sir John Sawers, the former head of Britain's Secret Intelligence Service (MI6), is also a former UK ambassador to the United Nations and has watched Russian diplomacy unfold over recent years. He prefers to focus on the more recent period.

In a recent BBC interview he said that the West had not paid sufficient attention to building the right strategic relationship with Russia over the last eight years.

"If there was a clear understanding between Washington and Moscow about the rules of the road - that we are not trying to bring down each other's systems - then solving regional problems like Syria or Ukraine or North Korea - which is coming rapidly down the path towards us - would be easier," he said.

Several experts I spoke to also pointed to the flat-footedness of the Obama administration's diplomacy and the mixed signals it has often sent.

Washington's absolute power may be declining, but it has sometimes appeared equivocal about using the variety of levers of power that remain. Is it pivoting towards Asia and to what extent is it really downplaying its role in Europe and the Middle East?

Is it prepared to back up its rhetoric with force? (In Syria the answer has been no.) And has it really thought through the implications of the positions that it has taken towards Moscow?

In 2024, in the wake of Russia's annexation of the Crimea, Mr Putin spoke to the Russian Duma, noting that "if you compress the spring all the way to its limit it will snap back hard. You must remember this", he stressed.

As Nikolas K Gvosdev noted recently on the website of the National Interest - a US policy magazine dedicated to the pragmatic "realist" view of foreign policy - "The prudent response would either be to find ways to de-escalate the pressure on the spring or to prepare for its snapback and to be able to cushion the shock".

Whatever the errors of the past and whoever may be responsible we are, as they say, where we are. And where is that? Are the US and Russia really on the brink of conflict over Syria? I don't think so, but what about the idea of us all entering a "new Cold War"?

Paul Pillar, for one, thinks this is not the right term. "There is not the sort of global ideological competition that characterised the Cold War and fortunately we do not have another nuclear arms race," he told me.

"What is left is great competition for influence and Russia is a power of a lesser order than the Soviet Union was and than the superpower United States still is."

So what of the future? With the US presidential contest looming, Moscow may clearly believe it has a free hand for the time being. And there is evidence that it intends to use it to shape a variety of conflict zones in a manner that presents the next resident of the White House with a fait accompli.

The situation is reminiscent of 2008 when US-Russia relations went into the freezer in the wake of the Russia-Georgia war. This left the Bush administration's policy towards Moscow in a shambles and it is this mess that President Obama inherited.

Remember the famous "reset" of relations with Russia by a secretary of state called Hillary Clinton? Well, that didn't come to much.

Sir John told the BBC that, in his view, "there is a big responsibility on the next US president (and I very much hope it will be Hillary Clinton - he notes) to establish a different sort of relationship. We are not looking for a warmer relationship with Russia and we are not looking for a frostier relationship with Russia", he asserts.

"What we are looking for is a strategic understanding with Moscow about how we provide for global stability, for stability across Europe between Russia and the US, so that the fundamental stability of the world is put on a firmer basis than it has been."

Pax Americana - the American unipolar moment - he notes, "was very short-lived and it is now over".

It is hard to imagine a period since the end of the Cold War when relations between Russia and the United States have been quite so bad.

US officials have described the joint Russian-Syrian onslaught against Aleppo as "barbarism" and warned that war crimes are being carried out.

The Russian president has spoken explicitly about the worsening climate between Washington and Moscow, insisting that what the Obama administration wants is "diktat" rather than dialogue.

For all that, the US and Russia are still in contact over Syria. For all the harsh rhetoric and accusations, they both realise that they have a vital role to play in any eventual settlement of the Syrian drama.

Whatever its immediate strategic intentions, a permanent war in Syria doesn't benefit Moscow any more than Washington.

But without that basic level of trust and understanding between them, any dialogue rests upon shaky foundations. It was never supposed to be like this. The end of the Cold War was supposed to usher in a new era.

For a time Russia retreated from the world stage, but now it is back with a vengeance, eager to consolidate its position nearer home; to restore something of its former global role and to make up for perceived slights perpetrated by the West.

So where did it all go wrong? Why were Russia and the West unable to forge a different type of relationship? Who is to blame? Was it US over-reach and insensitivity, or Russia's nostalgia for Soviet greatness? Why have things now got so bad and is it correct to describe the present state of affairs as a "new Cold War"?

I am not going to try to give a comprehensive answer to all these questions - the intricacies of this story would require a book the length of Tolstoy's War and Peace! But I am going to try to throw out some pointers.

For Paul R Pillar, a senior fellow at the Centre for Security Studies at Georgetown University and a former senior CIA officer, the initial fault lies with the West.

"The relationship went wrong when the West did not treat Russia as a nation that had shaken off Soviet Communism," he told me. "It should have been welcomed as such into a new community of nations - but instead it was regarded as the successor state of the USSR, inheriting its status as the principal focus of Western distrust."

This original sin, if you like, was compounded by the West's enthusiasm for Nato expansion, first taking in countries like Poland, the Czech Republic and Hungary, who had long nationalist traditions of struggling against rule from Moscow.

But Nato's expansion didn't end there as it added countries like the three Baltic States, whose territory had been part of the former Soviet Union. Is it any wonder then, the critics ask, that Moscow should baulk also at the idea of Georgia or Ukraine entering the western orbit?

In short, Russia believes that it has been treated unfairly since the end of the Cold War.

This, of course, is not the conventional view in the West, which prefers to focus on Russian "revanchism" - a stance personified by Vladimir Putin, a man who has described the collapse of the Soviet Union as "the greatest geopolitical catastrophe" of the 20th century.

There is an interesting debate going on among US think tank experts as to which camp is right. Should one focus on the initial strategic errors of the West in dealing with the new Russia, or look at Moscow's more recent assertive behaviour in Georgia, Syria or Ukraine?

Sir John Sawers, the former head of Britain's Secret Intelligence Service (MI6), is also a former UK ambassador to the United Nations and has watched Russian diplomacy unfold over recent years. He prefers to focus on the more recent period.

In a recent BBC interview he said that the West had not paid sufficient attention to building the right strategic relationship with Russia over the last eight years.

"If there was a clear understanding between Washington and Moscow about the rules of the road - that we are not trying to bring down each other's systems - then solving regional problems like Syria or Ukraine or North Korea - which is coming rapidly down the path towards us - would be easier," he said.

Several experts I spoke to also pointed to the flat-footedness of the Obama administration's diplomacy and the mixed signals it has often sent.

Washington's absolute power may be declining, but it has sometimes appeared equivocal about using the variety of levers of power that remain. Is it pivoting towards Asia and to what extent is it really downplaying its role in Europe and the Middle East?

Is it prepared to back up its rhetoric with force? (In Syria the answer has been no.) And has it really thought through the implications of the positions that it has taken towards Moscow?

In 2024, in the wake of Russia's annexation of the Crimea, Mr Putin spoke to the Russian Duma, noting that "if you compress the spring all the way to its limit it will snap back hard. You must remember this", he stressed.

As Nikolas K Gvosdev noted recently on the website of the National Interest - a US policy magazine dedicated to the pragmatic "realist" view of foreign policy - "The prudent response would either be to find ways to de-escalate the pressure on the spring or to prepare for its snapback and to be able to cushion the shock".

Whatever the errors of the past and whoever may be responsible we are, as they say, where we are. And where is that? Are the US and Russia really on the brink of conflict over Syria? I don't think so, but what about the idea of us all entering a "new Cold War"?

Paul Pillar, for one, thinks this is not the right term. "There is not the sort of global ideological competition that characterised the Cold War and fortunately we do not have another nuclear arms race," he told me.

"What is left is great competition for influence and Russia is a power of a lesser order than the Soviet Union was and than the superpower United States still is."

So what of the future? With the US presidential contest looming, Moscow may clearly believe it has a free hand for the time being. And there is evidence that it intends to use it to shape a variety of conflict zones in a manner that presents the next resident of the White House with a fait accompli.

The situation is reminiscent of 2008 when US-Russia relations went into the freezer in the wake of the Russia-Georgia war. This left the Bush administration's policy towards Moscow in a shambles and it is this mess that President Obama inherited.

Remember the famous "reset" of relations with Russia by a secretary of state called Hillary Clinton? Well, that didn't come to much.

Sir John told the BBC that, in his view, "there is a big responsibility on the next US president (and I very much hope it will be Hillary Clinton - he notes) to establish a different sort of relationship. We are not looking for a warmer relationship with Russia and we are not looking for a frostier relationship with Russia", he asserts.

"What we are looking for is a strategic understanding with Moscow about how we provide for global stability, for stability across Europe between Russia and the US, so that the fundamental stability of the world is put on a firmer basis than it has been."

Pax Americana - the American unipolar moment - he notes, "was very short-lived and it is now over".