It is 20 years since the attempted coup against Soviet leader Mikhail Gorbachev. It failed, but new BBC interviews underline how fragile his hold on power had become - and how quickly and informally the eventual decision to disband the USSR was taken.
The attempted Moscow coup of August 1991 did not come completely out of the blue.
At the start of the year, Soviet troops had tried to storm the parliament in Lithuania, apparently hoping to force the breakaway republic back under central control.
It was obvious the order came from Moscow. Less clear, though, was how far President Gorbachev was involved.
At the time, he was evasive about his role. Now he admits that the attack happened behind his back, organised by hardline opponents in his own government. It was a sign that his power was slipping away.
"I never gave them permission to impose martial law or presidential rule. They took the decision," Mr Gorbachev says.
"People don't realise that the worst thing for me was that I didn't know."
The US government was acutely aware of how incendiary the whole issue of nationalism in the 15 Soviet republics was and how difficult it would be for Mr Gorbachev to allow the Baltic states to follow Eastern Europe in breaking free.
"He would have been accused of treason," says the US Ambassador to Moscow, Jack Matlock, looking back. "If he had agreed to this, the military and the party would have removed him.
"You know, if a coup attempt had occurred earlier than it did, it could well have been successful. At any time in 1990, there could have been a successful coup against him."
Nonetheless, the attempt to re-impose Moscow rule on Lithuania alarmed the Americans.
President George Bush despatched Ambassador Matlock to the Kremlin to warn Mr Gorbachev that further violence would affect US-Soviet relations.
"He listened carefully," Matlock recalls. "And then he said: 'Jack, please explain to your president, this country is on the brink of civil war. And as president I must do all I can to prevent that. And that means I'm going to have to zig and zag. My goals are the same. Please reassure your president and help him understand'."
Mr Gorbachev was under pressure from other quarters, too. For ordinary people, economic upheaval was beginning to make life unbearable.
Mr Gorbachev took the brunt of their rage.
Sir John Major, British prime minister at the time, recalls Mr Gorbachev wryly recounting a joke.
"He smiled and told me the following story: there was a food shortage in Moscow and people were queuing for bread. They'd been queuing a long time and they were getting very irritated.
"And one man turned in the queue to his neighbour and said: 'I'm fed up with this, I blame Gorbachev, I'm going to kill Gorbachev,' and off he went. He came back two days later and the people in the queue said: 'Did you kill Gorbachev?' 'No,' he replied 'The queue to kill Gorbachev was just too long'."
Mr Gorbachev also faced the emergence of a powerful pro-reform opponent.
Boris Yeltsin, once his political protege, was now Russian president, a new post which he had won by a landslide in popular direct elections.
Mr Gorbachev, by contrast, was elevated to the position of Soviet president only by the Soviet parliament, not the people, so could not lay claim to a similar mandate.
Looking back, Mr Gorbachev cannot conceal his bitterness towards Yeltsin.
"I made a mistake," says Mr Gorbachev now, "I should have got rid of him. It was because of Yeltsin that events unfolded as they did."
In late June 1991, the Americans got a tip off that Mr Gorbachev's own security and defence ministers might be planning a coup against him.
Once again, it was Ambassador Matlock who went to warn the Soviet president.
"I told him: 'We have information which we cannot confirm, but it's more than a rumour, that a coup is being organised against you and it could happen at any time'," remembers Mr Matlock.
"But he didn't take it seriously. As a matter of fact he actually laughed, turned to his assistant, who was the only other person in the room, and said something about naive Americans."
But the rumour was correct.
In mid-August the coup plotters decided to act. The catalyst, it seems, was a private conversation they overheard between Mr Gorbachev, Boris Yeltsin and the president of Kazakhstan.
The men were conferring on plans for a new Union Treaty to be signed on 20 August, which would overhaul relations between the republics and central government - and they had talked openly about the opponents in government they would need to remove from office.
What Mr Gorbachev and his colleagues did not realise was that the plotters were listening in - a stupid mistake, says Mr Gorbachev.
"Kryuchkov, the KGB chief, was recording us. He gave the tape to Yazov, the defence minister, to listen to. And then the others, too. In a word, they all took fright and concluded they had nothing to lose. So they decided to go for a coup d'etat."
The coup plotters' first plan was to co-opt Mr Gorbachev. A delegation flew down to the Black Sea villa where he was taking a weekend break to give him an ultimatum: either declare a state of emergency or else hand over power.
Mr Gorbachev says he realised something was wrong even before they arrived.
"I started to pick up phones, and not a single one was working. Not a single telephone was working. They cut me off and isolated me as they were approaching, so that I would not be able to contact anyone."
According to one version of events, his response to the plotters was evasive. But Mr Gorbachev tells a different story.
"When I realised what was about to happen, I called in my wife Raisa, our daughter and son-in-law and said: 'Look, very dangerous events are about to unfold. I cannot go for a compromise with them, and you must know this.' They said whatever happened, they'd be with me till the end."
Then he says the delegation walked in and an angry exchange followed.
"I even swore at them," says Mr Gorbachev. "I said 'Go and convene a Congress… and we'll see whose plan gets more support, yours or mine'."
The plotters flew back to Moscow empty-handed to enact the state of emergency without him, while Mr Gorbachev and his family were left under house arrest, unsure whether they could even trust their bodyguards.
In Moscow, Mr Gorbachev was seen as an absent, passive victim. Resistance to what turned out to be an abortive coup was led by Boris Yeltsin and supported by thousands of ordinary citizens and some members of the military, who refused to obey orders to turn on their own people.
When Mr Gorbachev and his family returned to Moscow after it was all over, some three days later, it soon became clear that power had shifted.
Boris Yeltsin was asserting his right to rule Russia. Other leaders were taking similar steps in other republics.
In December 1991, Yeltsin suggested to the presidents of Ukraine and Belarus, Leonid Kravchuk and Stanislav Shushkevich, that they should meet separately to talk about the future without Mr Gorbachev, who was still trying to hammer out a new Union Treaty.
At an informal gathering in Belarus, they decided to dissolve the Soviet Union.
Stanislav Shushkevich remembers it as an almost impromptu decision.
"Yeltsin said, 'Would you agree for the Soviet Union to end its existence?' I said OK and Kravchuk said OK too.
"It only really dawned on me afterwards, when my car came to take me home what we'd done.
"I was thinking, 'Tomorrow I need to present this to the Belarus parliament and they could throw it out, because this is a momentous thing we've done'."
They also, of course, had to inform the outside world.
Mr Shushkevich says it was decided he would call Mr Gorbachev while Yeltsin phoned the US president.
"When they finally put me through to Gorbachev, Yeltsin was already on the phone to Bush.
"So I told Mikhail Sergeyevich (Gorbachev) and he said: 'Can you imagine what the outside world will think of this?' In other words: 'You idiots for getting involved in this.'
"And I said, 'Well, actually, Yeltsin is speaking to President Bush right now.'
"On the other end of the phone there was a silence, and then Mr Gorbachev hung up."
Mr Gorbachev had no choice but to resign. After six years in power, he stood down at the end of December 1991, just before the Soviet Union ceased its existence. He handed over all the relevant papers and authorities to Boris Yeltsin. The two men never spoke again.
To this day, Mr Gorbachev is scathing about him.
"This is an epic story with Boris Nikolayevich Yeltsin as its main character. He's a scoundrel and a traitor. We sat down and agreed how things would be. Then when we'd parted to set in motion what we'd agreed, he began scheming behind my back. He was a traitor."
Gorbachev: The Great Dissident can be seen globally, on BBC World News at 09:30 and 21:30 GMT on Saturday 20 August (check BBC World News TV schedules for local screening times).
In the UK, Part One can be seen on the BBC News Channel on Saturday 20 August at 02:30, 05:30, 14:30 and 21:30 BST, with Part Two screening on Sunday 21 August at 03:30, 10:30, 14:30 and 23:30 BST.
Reporter: Bridget Kendall. Producer and Director: Ewa Ewart