Dobson is guest-blogging for The Post.

This, too, began in the least likely of places. On December 17, 2010, local officials harassed Mohamed Bouazizi, a fruit vendor in the Tunisian city of Sidi Bouzid. Ashamed, angry, and pushed beyond what he could accept, Bouazizi took his own life in a public act of self-immolation. Since Bouazizi died from his burns in early January, we have all watched as one uprising begat another. First, the authoritarian duchy of Tunisia fell. Then, came the revolution in Egypt, the epicenter of the Middle East. Massive protests sprang up in Bahrain and Yemen, just as Libya descended into carnage, followed by outright civil war. The tremors have been felt in Algeria, Jordan, Oman, Saudi Arabia and Sudan. Yesterday, protesters began a fourth day of demonstrations in Syria, one of the region’s most repressive states. Major elements of the Yemeni military are defecting from the regime and joining the demonstrators. A fruit vendor takes his own life—and a region is turned upside down. Is this the beginning of the Fourth Wave?

It’s impossible to say for sure, since we are still in Act I of an unfolding drama. Surviving regimes, as we are seeing, are not conceding as quickly as was the case in Tunisia and Egypt. But if we want to plumb whether this might be a democratic wave in the making, we should ask ourselves, “Why now?”

Last month, in Beijing, I posed this question to nearly a dozen members of the Chinese Communist Party who are tasked with thinking about international politics. One of the more honest among them admitted that the party has no idea why this is happening right now. An expert of the Middle East, he told me that we “don’t even know what to call these revolutions because we can’t settle on the precise cause.”

I posed the same question last week in Cairo — “why now?” — to Mohamed Adel, a youth leader in the April 6th Movement, which helped lead the charge against Hosni Mubarak. He pointed to the growing number of protests in recent months. He mentioned the outright rigging of the November elections. He noted a change in some youth groups’ tactics. When he stopped listing the reasons, I looked at him and said, “Was there any other reason why this happened now?”

 “Oh yes, and Tunisia. Of course, Tunisia,” he said.

There is no question that all the factors that Adel rattled off—and others he didn’t—played a part. But many of these factors have been in place for years. The November elections weren’t the first rigged polls. If you put labor protests aside, Egypt saw a greater season of political protests in 2005 and 2006 than in 2010. The change in tactics by youth groups is enormously important, but so is the fact that people felt confident enough to join them. Sure, society was boiling, but it hadn’t boiled over. The element that had to change was the collective fear that kept Egyptians from coming out in force. And when Egyptians witnessed what the Tunisian people had accomplished — forcing Zine el-Abidine Ben Ali to make a mad dash for the airport after two decades as dictator — that fear began to fall away. It is what political scientists like Huntington call a “demonstration effect.” The Tunisians demonstrated to Egyptians, and for that matter all Arabs, what was possible.

We have all known that Arab autocracies have been miserable, repressive, under-performing places for years. Yet no experts whom I know were ready to call them ripe for revolution. The regimes were just too strong, the security apparatus too oppressive. But the speed at which these uprisings have spread suggests that the factor that may matter most in answering the question “why now?” is a visceral one, something almost instantaneous. Political scientists will argue about this for decades, but I am putting my money on the “demonstration effect.” In an age where everything is on public display, nothing is more powerful than a demonstration of what is possible.

One other thing is probably true. It took nearly 15 years for Huntington to be able to confidently identify the Third Wave. My guess is that if we are at the beginning of a Fourth Wave, we will know much sooner.