Two decades after the fall of Soviet-bloc dictatorships, popular movements for democracy are erupting in the last regional bastion of authoritarianism: the Arab world.

So far, only Tunisia's dictator, Zine el-Abidine Ben Ali, has been toppled, while Egypt's President Hosni Mubarak - who has ruled that ancient land longer than many pharaohs - announced Tuesday that he will step down in September. But other Arab autocrats are bound to go. From Algeria to Syria to Jordan, people are fed up with stagnation and injustice, and are mobilizing for democratic change.

So, what happens when the autocrat is gone? Will the end of despotism give way to chaos - as happened when Mobutu Sese Seko was toppled in 1997 after more than 30 years in power in Zaire? Will the military or some civilian strongman fill the void with a new autocracy - as occurred after the overthrow of Arab monarchs in Egypt and Iraq in the 1950s, and as has been the norm in most of the world until recently? Or can some of the Arab nations produce real democracy - as we saw in most of Eastern Europe and about half the states of sub-Saharan Africa? Regime transitions are uncertain affairs. But since the mid-1970s, more than 60 countries have found their way to democracy. Some have done so in circumstances of rapid upheaval that offer lessons for reformers in Tunisia, Egypt and other Arab countries today.

Unite the democratic opposition.

When a dictatorship is on the ropes, one thing that can rescue it is a divided opposition. That is why autocrats so frequently foster those divisions, secretly funding a proliferation of opposition parties. Even extremely corrupt rulers may generate significant electoral support - not the thumping majorities they claim, but enough to steal an election - when the opposition is splintered.

In the Philippines in 1986, Nicaragua in 1990 and Ukraine in 2004, the opposition united around the candidacies of Corazon Aquino, Violeta Chamorro and Viktor Yushchenko, respectively. Broad fronts such as these - as well as the Concertacion movement that swept Christian Democrat Patricio Aylwin to power in Chile in 1989 after the departure of Gen. Augusto Pinochet - often span deep personal and ideological differences. But the time for democratic forces to debate those matters is later, once the old order is defeated and democratic institutions have been established.

Egypt is fortunate - it has an obvious alternative leader, Mohamed ElBaradei, whom disparate opposition elements seem to be rallying around. Whether the next presidential election is held on schedule in September or moved up, ElBaradei, or anyone like him leading a broad opposition front, will probably win a resounding victory over anyone connected to Mubarak's National Democratic Party.

Make sure the old order really is gone.

The exit of a long-ruling strongman, such as Ben Ali, does not necessarily mean the end of a regime. Fallen dictators often leave behind robust political and security machines. No autocrat in modern times met a more immediate fate than Romania's Nicolae Ceausescu, who was executed by a firing squad of his own soldiers in 1989 just three days after a popular revolution forced him to flee the capital. Yet his successor, Ion Iliescu, was a corrupt former communist who obstructed political reform. Most of the former Soviet states, such as Georgia and Kazakhstan, had similar experiences.

Countries are much more likely to get to democracy quickly if they identify and embrace political leaders who are untainted by the old order and are ready to roll it back.

But also come to an understanding with the old order.

Victorious democrats won't be able to completely excise the pillars of the authoritarian order. Instead, for their country to turn toward democracy, those pillars must be neutralized or co-opted. This old order may descend into violence when, as in Iraq, broad classes of elites are stigmatized and ousted from their positions. In a successful bargain, most old-regime elites retain their freedom, assets and often their jobs but accept the new rules of the democratic game.

Unless the military collapses in defeat, as it did in Greece in 1974 and in Argentina after the Falklands War, it must be persuaded to at least tolerate a new democratic order. In the short run, that means guaranteeing the military significant autonomy, as well as immunity from prosecution for its crimes. Over time, civilian democratic control of the military can be extended incrementally, as was done masterfully in Brazil in the 1980s and in Chile during the 1990s. But if the professional military feels threatened and demeaned from the start, the transition is in trouble.

The same principle applies to surviving elements of the state security apparatus, the bureaucracy and the ruling party. In South Africa, for example, old-regime elements received amnesty for their human rights abuses in exchange for fully disclosing what they had done. In this and other successful transitions, top officials were replaced, but most state bureaucrats kept their jobs.

Rewrite the rules.

A new democratic government needs a new constitution, but it can't be drawn up too hastily. Meanwhile, some key provisions can be altered expeditiously, either by legislation, interim executive fiat or national consensus.

In Spain, the path to democratization was opened by the Law for Political Reform, adopted by the parliament within a year of dictator Francisco Franco's death in 1975. Poland adopted a package of amendments in 1992, only after it had elected a new parliament and a new president, Lech Walesa; a new constitution followed in 1997. South Africa enacted an interim constitution to govern the country while it undertook an ambitious constitution-writing process with wide popular consultation - which is the ideal arrangement.

An urgent priority, though, is to rewrite the rules so that free and fair elections are possible. This must happen before democratic elections can be held in Egypt and Tunisia. In transitions toward democracy, there is a strong case for including as many political players as possible. This requires some form of proportional representation to ensure that emerging small parties can have a stake in the new order, while minimizing the organizational advantage of the former ruling party. In the 2005 elections in Iraq, proportional representation ensured a seat at the table for smaller minority and liberal parties that could never have won a plurality in individual districts.

Isolate the extremes.

That said, not everyone can or should be brought into the new democratic order. Prosecuting particularly venal members of a former ruling family, such as those tied to the Philippines' Ferdinand Marcos, Indonesia's fallen strongman Suharto or now Tunisia's Ben Ali, can be part of a larger reconciliation strategy. But the circle of punishment must be drawn narrowly. It may even help the transition to drive a wedge between a few old-regime cronies and the bulk of the establishment, many of whom may harbor grievances against "the family."

A transitional government should aim for inclusion, and should test the democratic commitment of dubious players rather than inadvertently induce them to become violent opponents. However, groups that refuse to renounce violence as a means of obtaining power, or that reject the legitimacy of democracy, have no place in the new order. That provision was part of the wisdom of the postwar German constitution.

Transitions are full of opportunists, charlatans and erstwhile autocrats who enter the new political field with no commitment to democracy. Every democratic transition that has endured - from Spain and Portugal to Chile, South Africa and now hopefully Indonesia - has tread this path.

Fragile democracies become stable when people who once had no use for democracy embrace it as the only game in town.