The sheer experience of tens of thousands of people on the streets together builds confidence in what they can do, far beyond the point where they can be bought off by half-measures or controlled by any ordinary police operation, writes Charles Richardson. Revolutions go in and out of fashion. The mid-20th century was a lean period -- the bad experience of the Russian Revolution of 1917 discredited the idea for a while -- but revolutionary fervor returned in Portugal in 1975, the Philippines in 1986 and, of course, the springtime of eastern Europe in 1989. Now another wave seems to be under way, with first Tunisia and now Egypt showing that the people of the Arab world, when conditions are ripe, are equally capable of taking matters into their own hands. Every country, and therefore every revolution, is different, but nonetheless there are similarities in how they work. And all of our experience suggests that Egypt has now reached the point of no return: that the only remaining options are total regime change or massive repression. Once popular discontent reaches this scale, it is incredibly powerful. The sheer experience of tens of thousands of people on the streets together builds confidence in what they can do, far beyond the point where they can be bought off by half-measures or controlled by any ordinary police operation. Revolutionary movements can be stopped, but only by a leadership that is ruthless about using armed force and willing to kill large numbers of its citizens. The Burmese generals did it in 1988, as did Deng Xiaoping in 1989 and the theocrats of Iran in 2009. The decision Hosni Mubarak has to make -- and soon -- is whether or not to try to emulate them. His record suggests that Mubarak would have few moral qualms about attempting a "Chinese solution". But that is not his only consideration; repression doesn't always work, and if it fails the consequences are likely to be much more serious. Ferdinand Marcos, who blinked under pressure, ended his days in tranquil exile in Hawaii; Nicolae Ceausescu, who tried to fight it out, ended up in front of a firing squad. Crucially, repression depends on the loyalty of the armed forces. The army in Egypt is still popular, and the opposition has expressed confidence that it will not turn its guns on them. Overnight a statement from the army made that official, promising "The armed forces will not resort to use of force against our great people" and affirming "that freedom of expression through peaceful means is guaranteed to everybody". Pessimists will recall a similar confidence shown by the revolutionaries in the weeks before Tiananmen Square, which turned out to be fatally mistaken. But there is a key difference between Egypt and the recent cases of countries that have successfully crushed a popular uprising: none of them were American allies. Egypt's armed forces have been bankrolled by the US for 30 years, and its commanders are used to the idea that their interests are closely tied up with American approval. Even if Mubarak is willing to defy his paymasters, it seems unlikely that his generals will go along - at the best of times, professional soldiers dislike the idea of firing on unarmed civilians. For the Obama administration, this is a delicate task to manage. No government anywhere likes to be seen to be pulling the rug out from under an ally, and Obama will particularly have in mind the example of Jimmy Carter, who was vilified by his political opponents for "losing" both Iran and Nicaragua, after belatedly withdrawing American support from their threatened autocrats. The American response to Egypt has given the impression of scrambling to keep up, and sending mixed messages as a result, but this may be partly due to the fear of being too explicit. Privately, Obama probably realises that Mubarak is doomed, but to convey that message openly would risk being counter-productive. And even relatively subtle American pressure can be effective, as was the Reagan administration in inducing Marcos to leave quietly. Whatever its hesitations, American policy has at least been commendably clear in warning against the use of force. But without force, and plenty of it, the Mubarak regime is doomed.