Leading article: The democratic world must stand with the Egyptian protesters

The three-decade long rule of Hosni Mubarak over Egypt was crumbling last night. The old dictator, confronted by an unprecedented wave of popular protests and strikes, was not prepared to go without a struggle. First he tried to divide the protesters, announcing his intention to step down as president later in the year. When that failed to disperse the crowds, Mr Mubarak is believed to have sent state-sponsored thugs to attack the pro-democracy protesters in Cairo's Tahrir Square.

Mr Mubarak's allies abroad tried their best to prop up the Egyptian strongman too. Frank Wisner, the veteran diplomat sent by Barack Obama to deal with the Egyptian regime, was arguing a week ago that Mr Mubarak "must stay in office". We learned yesterday that Saudi Arabia's King Abdullah pressured the White House to support Mr Mubarak, even threatening to replace any financial aid to Egypt withdrawn by the US. The Italian prime minister, Silvio Berlusconi, praised the Egyptian autocrat as a "wise man".

But the efforts of Mr Mubarak and his powerful friends have been insufficient. After 17 days of demonstrations, the Egyptian protesters seem to have achieved their primary goal: the departure of Mr Mubarak from the political stage. It is an astonishing achievement. Only a few months ago, Egyptians were grimly joking that Mubarak would die in office. Many assumed the presidency would, at that point, pass to Mr Mubarak's son, Gamal. Whatever happens next, the Mubarak dynasty looks over.

There was jubilation among many Egyptians last night, but also uncertainty. There were rumours that power would be transferred to the Egyptian vice-president, Omar Suleiman. The former head of the brutal intelligence services does not seem a vast improvement on Mr Mubarak. His remarks, earlier this week, that Egypt is "not ready" for democracy do not indicate a reformer.

The game finally ended for Mr Mubarak when the army pledged their support to the "legitimate demands" of protesters yesterday. Yet this raises the question: is this a democratic revolution, or a military coup? Will the army – the most powerful institution in Egypt – step back and allow democratic elections to take place? Or will they attempt to control events? Egyptians would be naive to imagine that the departure of Mr Mubarak is any guarantee that democracy will flow into the space left. Repressive regimes are sustained by more than one individual. They endure because they become self-sustaining networks of brutality and corruption. That network, like Mr Mubarak, will not go quietly.

The departure of Mr Mubarak is a test for western governments. Having sent mixed messages about their support for Egyptian reformers over the past fortnight, western leaders need to make it clear that they will throw their full support behind the pro-democracy movement and push for free elections and a credible new constitution. Barack Obama and European leaders must make it clear that there will be no more support for repressive autocrats who guarantee "stability". Goodwill in Egypt has already been lost through their vacillation. It would be disastrous to relinquish any more.

It is impossible to predict the effect on the region of these events. But there will certainly be repercussions. The autocrats of Riyadh are plainly deeply rattled. The repressive rulers of Syria, Jordan, Algeria and Libya will know that if the Egyptian regime can be overturned, with all its military and financial aid from the United States, it can happen anywhere. The oppressed people of the Arab world have now watched two revolutions in three months unfold in splendid detail, in large part thanks to the Al-Jazeera news channel. The Arab revolution looks anything but over.