By Paul Reynolds
World Affairs correspondent, BBC News website
The Israeli withdrawal from Gaza - and the wider disengagement plan of which it is part - represents a major shift in the political landscape of the Middle East of a kind that is seen only every decade or so.
Given Ariel Sharon's history, his Gaza plan stunned many observers
It remains to be seen whether it also represents an opportunity to clear the way for a final two-state agreement or is an attempt by Israeli Prime Minister Ariel Sharon to take matters into his own hands and draw Israel's final borders unilaterally.
Given the way that facts on the ground in the Middle East tend to determine the politics, the betting has to be that, without a major push by the United States and major concessions by each side, Mr Sharon's circling of the wagons will be the shape of things to come for the next decade.
At the end of the disengagement process, Mr Sharon will have got out of Gaza, often regarded as an optional extra even by settlers who think of the West Bank as Judea and Samaria and Israel's by right either by gift from God or by right of conquest in war.
He will have evacuated four small settlements in the northern West Bank but will have consolidated existing major settlement blocs (Ariel, Maale Adumim and others), which the Bush administration now accepts will not be given up.
He will also have constructed a barrier, some of it encroaching into what is regarded by the rest of the world as Palestinian territory, which will became a new de facto border or at least a line of demarcation.
East Jerusalem, sought by the Palestinians as their capital, will be included within it.
About 10% of land beyond the "green line" that marks the borders between 1949 and 1967 will be enclosed by the barrier, which is in parts a wall and in parts a fence.
It came as a surprise that Mr Sharon should have moved in this way.
Aluf Benn, diplomatic editor of the Israeli newspaper Haaretz, wrote in Foreign Affairs magazine in May that he had been wrong about Ariel Sharon in an earlier essay in 2002.
"I underestimated both his political survivability and his willingness to break away from the status quo," Mr Benn said.
However, Mr Benn was not entirely wrong.
"The signs had been there all along; even my Foreign Affairs article mentioned: 'Israel may decide to draw its permanent borders unilaterally and lock up the Palestinians behind fences.' But if I could imagine that Sharon would want to hurt the Palestinians, the notion that the former 'bulldozer' of the Israeli settlement project would tear down his life creation was beyond belief."
And yet, one must remember that Mr Sharon was a general and at heart still seeks the decisive manoeuvre that brings victory. One can see that at play here.
His history is one of the big move - from his controversial command of Unit 101 against Palestinians in the West Bank in the 1950s, to his unauthorised attack in the Mitla Pass in the war of 1956, to his war-winning crossing of the Suez Canal in 1973, to his invasion of Lebanon in 1982.
In the disengagement plan, he is showing as much original thinking in defence as he did in attack.
He has a strong pragmatic streak and it worth remembering that by no means all Israeli settlers are inspired by religion.
I met Israel's then Minister of Science, Professor Yuval Ne'eman, at a settlement opening on some remote West Bank hilltop in the mid-1980s. We were sitting in a makeshift synagogue made out of a tent and I asked him if he was in favour of settlements for religious reasons. He replied that he was an atheist and wanted them for "national reasons". Israel, he said, needed them as a barrier.
Visions of a Jewish state
It is in keeping with this philosophy of security that Mr Sharon has put forward his plan. Security, in his view, has been redefined since the 1980s and now requires a repositioning of Israeli lines.
It is not just attacks by Palestinians that have led to this re-thinking.
There is the demographic factor. If Israel did nothing, it would be faced by 2025 with a Palestinian Arab majority in the territory it controls between the sea and the River Jordan.
Graham Usher, Jerusalem correspondent for the Economist magazine said recently: "Sharon has confronted the dilemma that Ben Gurion confronted in 1948 and that dilemma Ben Gurion summed up very clearly: 'We either have a Jewish state without the land of Israel or we have the land of Israel without a Jewish state.'
"What Ben Gurion chose was the Jewish state. Sharon believed he could have both. He now realises he can't. That is why he is in the process of repartitioning the West Bank."
The question following the Gaza withdrawal and the completion of the disengagement or separation plan is whether negotiations can take place with the Palestinians leading to an overall agreement.
Is Gaza a way back to the so-called road map which draws up a procedure for negotiations or it will be Gaza first and Gaza only?
One cannot be sanguine about this.
There are so many uncertainties. How strong will Hamas become in Gaza in elections that have to be held in due course? Is each side even ready for real talks? What about the basic Palestinian demands - over East Jerusalem for example, soon to be behind the barrier? What about Israeli demands for security?
One recalls that not so long ago, in 2000, under President Bill Clinton, the Israelis and Palestinians were actually negotiating control of the last 100 metres around the heart of the Old City.
That is so far away now.
And yet President Bush has, for the first time, laid down that it is US policy to have a Palestinian state. How far will he seek to implement this in the last years of his last term?