The stunning victories of Tunisians and Egyptians in ousting their entrenched dictators have set imaginations alight across the Middle East like nothing since Gamal Abdul Nasser's fiery anticolonial rhetoric in the 1950s.

"We assumed that if one day an uprising emerged, it would be at the hands of a bold leader. Another strongman to replace the ones we didn't like," wrote popular Jordanian blogger Naseem Tarawnah in a letter of thanks to the Egyptian people. "Never, in our wildest imaginations, did we think this uprising would come from the people. Whatever happens, this ... is something no one can take away from them, or from us. It has been embedded in our memories."

Now, the beleaguered ship of Middle Eastern autocracy is under an assault unparalleled since the post-World War II revolutions that brought independence to much of the region.

Tunisia was the first shot across the bow. But the upheaval in Egypt, the Arab world's largest country, has unleashed a volley of fire from Libya to Iran.

It is not so much the aspirations that are new, but a shared spirit of hope that success is possible against long odds. It's a feeling that is unlikely to dissipate quickly and could fundamentally reshape the region – though how democratic the changes will be remains to be seen.

"It would be wrong to say that Tunisia or Egypt ignited a new pattern of protest or generated new expectations ... they've existed, but the organizers in many of these countries sense a new opportunity," says Toby Craig Jones, a historian of the Middle East at Rutgers University in New Jersey.

"There's this talk about a new Pan-Arabism, a new nationalist moment – I'm not sure that's right yet, but there is a perception that people across international borders are aware they have a common experience and interests given the autocrats and economic challenges they share, so whatever it is that exists up in the stratosphere, it's meaningful," Dr. Jones adds, referring to the spirit of revolt in the region.

Protests pose quandary for US

Libya, Jordan, Yemen, Bahrain, and Iran have all witnessed democracy protests in recent weeks, throwing into disarray America's decades-old regional policy of supporting autocrats in exchange for stability.

Both the US and ally Israel are concerned by the prospect of states whose policies may be formulated based on the desires of their people – potentially giving fuller expression to Islamist forces – rather than the deals their rulers make with other nations.

But while pro-democracy protesters may have a bad word for US support of their dictators, they're mostly focused on the regimes at home.

The Arab world is far from homogeneous. There are different cultures, different dialects, and different economic factors at play. But Egypt has clearly created a new sense of what's possible.

Bahrain the most vulnerable

In Tunisia and Egypt, the military and ruling party appear to have bet that by sacrificing their dictators they could negotiate a transition in which their roles and privileges would be largely preserved.

How other states negotiate that quandary will do much to signal whether more revolutions will follow – and what results they will bring. Jones of Rutgers says he's not yet convinced that the current ferment will bring a a real democratic opening.

"It's not that I want to be right, it's just for reasons of historical precedent it's hard to be optimistic," he says. "Even in Egypt, the hard work remains in front of them, and often the people who start revolutions aren't the ones to finish them."

But Bahrain's Sunni monarchy looks particularly vulnerable in the face of an increasingly restless Shiite majority.

The tiny island nation, located in the Persian Gulf between Saudi Arabia and Iran, is home to the US Navy's Fifth Fleet and critical to broader regional operations – including deterrence of Iranian aggression.

The ruling Khalifa family, which has held absolute power for two centuries and enjoys close ties with the US, could find themselves in an existential fight.

King Hamad bin Isa al-Khalifa has been in power since 2002; the king's powerful uncle, Prime Minister Khalifa bin Salman al-Khalifa, has held his unelected post since the nation won independence in 1971.

Unlike Egypt's largely leaderless opposition, in Bahrain the Shiite opposition movement Al-Wafaq is well-organized. It has in recent years been willing to work for change from within the system – since the November elections, it has held nearly half of the seats in the lower house of parliament. But last week it suspended its participation in the largely symbolic parliament after security forces killed protesters.

"There is an interesting shift in the political language, there have been small numbers of people protesting in Bahrain for five years now, but the discourse was about implementing the political reform promises made over the past decade," Jones says. "That's shifted. Now they are carrying signs and shouting, 'Down with the Khalifas.' "

How other protests differ from Egypt

Crucial to the revolt's success in Egypt and Tunisia was that the Army was unwilling to ruthlessly suppress the protesters. There's no guarantee that Col. Muammar Qaddafi's army will stand aside in Libya.

In neighboring Algeria, which has promised to repeal a 19-year-old state of emergency in response to protests, the military chose a civil war after the ruling party canceled elections that the Islamic Salvation Front looked set to win in 1991. There is no guarantee they won't choose that route again.

Yemen, the region's poorest country, also lacks a unified political opposition. There, protests have remained small although they've taken on a harsher antigovernment tone since Mubarak's ouster. The use of social-networking websites – so crucial to starting protests in Egypt and Tunisia – is limited, and the young student protesters have yet to connect with the general population.

"The situation here is totally different from Egypt. Here in Yemen there are very few that use technology like Facebook, Twitter," says Hamid al-Shamy, an English literature student at Sanaa University. But that hasn't stopped hope from spreading. "I don't love politics. But the situation here causes me to go out," he says. "What happened in Egypt and Tunisia made me think this could happen in Yemen. Here we needed it more."

Jordan is not Egypt, but Syria may be

Jordan, the only Arab nation apart from Egypt that has made peace with Israel, seems a less likely candidate for fast change. King Abdullah II still has a fair degree of legitimacy in the eyes of important sectors of his public,

"We all know that Jordan is not Tunisia and it's not Egypt," says Nimer al-Assaf, deputy general secretary of the Islamic Action Front, the political wing of the Muslim Brotherhood. "Our regime here is not like any other regime in the Arab countries ... [it] has never been an aggressive or bloody regime at all." In recent discussions between Islamic party leaders and the king, he adds, the protests in Egypt and Tunisia didn't even come up.

In Syria, with a far more ruthless regime than the Jordanian Hashemites, there is optimism – but also caution.

"The similarities between Syria and Egypt are very frightening and so we can't fail to take lessons," says a Syrian democracy activist who asked not to be identified out of fear of regime retaliation. "The propaganda – including the positioning of foreign policy as resistance [against the West] – is better here and [the] regime is keener to keep control. Poverty is also not yet at the levels of Egypt. But give it two years and we might be ready for something similar."