In its way the overthrow of President Hosni Mubarak is as significant as the collapse of the Soviet bloc in Eastern Europe back in 1989.
That showed that a system which seemed to be fixed and stable and likely to endure for decades was in fact brittle and fragile. Egypt's military dictatorship has been shown to be similarly feeble.
It took just 18 days to overthrow a proud, elderly man who had pitted himself stubbornly against the will of millions of Egyptians.
Egypt's army found itself right in the middle, unwilling until the very end to force President Mubarak to go, yet deeply opposed to clearing the demonstrators out of Tahrir Square by sheer force.
So why has Mr Mubarak gone now after insisting that he would stay until the presidential elections in six or seven months time?
Two main reasons. The Americans - who had been embarrassed, helpless, onlookers - finally summoned up all their power and influence to force the Egyptian military to get rid of Mr Mubarak.
But there was something else. The military leaders realised that cracks were starting to appear in the army's structure. Many junior officers, ordinary soldiers, sided with the demonstrators. The generals backed the president who was one of their own.
There is a historical echo to this. In the 1952 revolution against the monarchy, some senior officers supported the king, while younger ones like Colonel Gamal Abdul Nasser backed the coup.
Nasser became president after sweeping his boss, General Naguib, aside. Since Nasser, there has only been two presidents in Egypt, Anwar Sadat and Hosni Mubarak.
For sixty years this country has been a military dictatorship backed by a nasty secret police force. Finally, no doubt reluctantly, the army leaders have brought Nasser's system to an end.
It would never have happened though had it not been for the tremendous fortitude of the tens of thousands of people who took control of Tahrir Square and refused to leave.
On Friday 28 January, the police attacked them with bricks, iron bars, and live ammunition.
They would not be budged.
When gangs of tough, determined Mubarak supporters were bussed in by the police and army to wrest control of the square from them, the demonstrators fought back with even greater ferocity.
The gangs slowly retreated and were eventually driven out of the side roads around the square - after that they disappeared altogether.
Right from the start the soldiers who were sent in to discourage the demonstrators from taking over the square showed themselves to be clearly sympathetic. That, in the end, proved decisive.
'Could happen anywhere'
The extraordinary scenes in Cairo tonight - with the streets, avenues, and bridges jammed with hooting cars and excited flag-waving people - are a sign of the relief and pride which the crowds now feel.
This was a victory for them in a country where people have habitually been obliged to do what their political masters told them.
Now they have the prospect of voting for their own leader in the coming presidential election.
In Egypt's 5,000 years as a unitary state, these people have never been able to choose their government before.
Will the army let it happen? It is hard to think now that they could prevent it. The people who have taken control of their cities and their country once know how to do it again. It would be foolhardy for the army to try to stop them.
What has happened here in Egypt can happen anywhere. In Libya, in Iran, in Algeria, in Syria. It does not take leaders and it does not take a well-organised conspiracy.
It simply takes courage of the kind the demonstrators have shown in Egypt.
The leaders of autocracies in the Middle East and way beyond should not sleep easy after this.