The toppling of the Tunisian regime led by Zine el-Abidine Ben Ali has led a lot of smart people -- including my FP colleague Marc Lynch -- to suggest that this might be the catalyst for a wave of democratization throughout the Arab world. The basic idea is that events in Tunisia will have a powerful demonstration effect (magnified by various forms of new media), leading other unhappy masses to rise up and challenge the stultifying dictatorships in places like Egypt or Syria. The obvious analogy (though not everyone makes it) is to the velvet revolutions in Eastern Europe, or perhaps the various "color revolutions" that took place in places like Ukraine or Georgia.
Color me skeptical. In fact, the history of world revolution suggests that this sort of revolutionary cascade is quite rare, and even when some sort of revolutionary contagion does take place, it happens pretty slowly and is often accompanied by overt foreign invasion.
For starters, the French revolution did not in fact ignite sympathetic revolutions across Europe. True, assorted monarchies were eventually toppled, but that was mostly done by the bayonets of the French army. Similarly, although many people feared that Bolshevism would spread across Europe after 1917, it did not in fact prove to be very contagious and the expansion of international communism didn't take place until World War II, once again largely backed by the might of the Red Army (or by indigenous communists like Mao Zedong, and only after decades of civil war). The Iranian revolution in 1979 did not prove to be an especially contagious model either; although sympathizers did emerge in several places (e.g., Lebanon), we've hardly seen a wave of Khomeini-style revolutions over the past 30 years.
The velvet revolution in Easter Europe are a partial exception, but mostly because the Soviet Union's Eastern Europe satellites were all dependent on the threat of Soviet invasion to keep their artificial regimes in power. Once the common keystone of Soviet power was no longer credible, however, all of these dominos could in fact fall down in a row.
But that's not the case in the Arab world. Although most Arab governments are authoritarian, they are also all independent and depend on a slightly different mix of political institutions and measures to keep the rulers in power. The fact that Ben Ali ultimately mismanaged a challenge and was driven from power does not mean that other Arab leaders won't be able to deflect, deter, or suppress challenges to their rule.
There are three other reasons why the Tunisian example is unlikely to lead to similar upheavals elsewhere. First, as Timur Kuran and others have shown, the actual revolutionary potential of any society is very difficult to read in advance, and a rising revolutionary wave often depends on very particular preferences and information effects within society. Put differently, whether a genuine upheavel breaks out and gathers steam is a highly contingent process. Second, Tunisia is an obvious warning sign to other Arab dictatorships, and they are bound to be especially vigilant in the months ahead, lest some sort of similar revolutionary wave begin to emerge. Third, Tunisia's experience may not look very attractive over the next few weeks or months, especially if the collapse of the government leads to widespread anarchy, violence and economic hardship. If that is the case, then restive populations elsewhere may be less inclined to challenge unpopular leaders, reasoning that "hey, our government sucks, but it's better than no government at all."
All of this is not to say that a cascade is impossible, that events in Tunisia won't exert a long-term effect on political discussion elsewhere, or that it is not a telling sign of democratic aspirations that are likely to bear fruit eventually. But "eventually" could be a rather long time, and if you are expecting to see a rapid transformation of the Arab world in the wake of these events, you're likely to be disappointed.
Stephen M. Walt is the Robert and Renée Belfer professor of international relations at Harvard University.