Hosni Mubarak's dramatic departure marks the end of an era for Egypt and the Middle East. Thirty years of his rule has left a deep impression on his country's domestic affairs and external relations. Without him, much could change on many fronts -- at home and across the region.
Egyptian politics, like all politics, are local, and what happens next depends crucially on the readiness of the military establishment to oversee what Barack Obama has called a genuine transition to democracy, in line with the thunderous demands of the now triumphant protestors massed in Cairo's Tahrir Square.
It was always likely that the army, the most powerful player in Egyptian politics since the 1952 revolution, would step in as the guardian of stability. The US, Israel and most other Arab regimes will most likely welcome that, keeping their qualms to themselves. So, for the moment, will many ordinary Egyptians - but only if it is the prelude to far-reaching change.
Rule by the military can only be temporary. Mubarak's exit, the dissolution of what is seen as an illegitimate parliament, constitutional reforms and abolition of the emergency laws are all non-negotiable. If those reforms are achieved, then Egypt will have witnessed a real revolution - beyond the removal of a stubborn 82-year-old president long past his sell-by date.
It seems clear from the events of recent days - especially the confusion and contradictory messages on Thursday -- that the army is divided. If it moves solely to protect its own privileged position, and that of the big businessmen who have done so well out of their links with the regime - then the system will not open up, at least not without large-scale repression and bloodshed.
Mubarak's replacement by the armed forces will mean a resumption of the talks that began earlier this week on constitutional and other changes, though they were pronounced dead almost before they began.
With good will it should be possible to amend or rewrite the constitution to allow the election of a new parliament and president. It could, however, all still take months to agree, risking impatience in the streets and new unrest.
Egypt's extraordinary change matters first for Egypt's 82 million people. But what happens in the Arab world's most populous country matters for many millions of other Arabs, who also suffer from unemployment, inequality, corruption and unresponsive, unaccountable governments - and share the language in which it is being covered in media such as al-Jazeera and social networking sites that official censors cannot easily block.
Other authoritarian regimes, shocked first by the uprising in Tunisia and now in Egypt, have been trying to pre-empt trouble by promises of reform, sacking ministers, maintaining subsidies or raising wages to buy off critics and defuse tensions. The symptoms are visible from Yemen to Jordan, from Algeria to Syria.
Egypt's political future also matters enormously to the US - thus the importance of the policy pronouncements from Washington since the crisis began, shown again by Obama's renewed call on for an "orderly and genuine transition" to the post-Mubarak era.
In the 1960s and 1970s, Egypt was a Soviet client, but it changed sides in 1979 by signing a taboo-breaking peace treaty with Israel, after four wars that cost it thousands of lives.
First under Anwar Sadat, and then under Mubarak, the relationship with the US blossomed to one of high-level strategic co-operation, so much so that Egyptian forces took part in the liberation of Kuwait after the Iraqi invasion in 1990.
Egypt remains a vital asset in allowing US military overflights, as the guardian of the strategically vital Suez canal, and a loyal ally in the regional confrontation with Iran.
Mubarak has played a key role in supporting the western-backed Palestinian Authority and containing the Islamist movement Hamas in the Gaza Strip, not least because of its affinity with the banned Muslim Brotherhood - whose likely future role in a freer Egyptian political system is a key and much-discussed issue both at home and abroad.
The events of the last 18 days have forced Obama to shift away from stability to embracing if not promoting democracy - to the evident discomfort of other conservative Arab friends, especially the Saudis. Jordan and Yemen share those concerns - fearing that unconditional US support for them may now also wane.
Israel has also let it be known in no uncertain terms that it prefers stability as the best guarantor of the peace treaty and as a barrier to Isalmist power and hinted that an Iranian-type revolution may be unfolding on the banks of the Nile.
But any realistic appraisal would conclude that the Egyptian military and security establishment as currently constituted has no interest in undermining its strategic relationships with either Washington or Tel Aviv - the latter in particular deeply unpopular with the mass of Egyptians. Signs of that outlook changing over time will be watched very closely.
