On March 3, Iranian President Mahmoud Ahmadinejad paid his first official visit to Saudi Arabia. Those who anticipated some dramatic outcome were disappointed. Not only were no concrete agreements announced; the summit with King Abdullah did not even produce the kind of anodyne communiqu that normally follows such meetings. That should not have been surprising. After all, while Iran and Saudi Arabia may share certain short-term interests, they embody the fundamentally conflicting forces that could potentially fuel a Middle Eastern clash of civilizations. The former is a Shi'ite and Persian-dominated republic ruled by a revolutionary Islamic regime bent on subverting the regional order, defying the United States, and challenging the existence of Israel; the latter is a Sunni and Arab monarchy ruled by a conservative Islamic regime bent on preserving the regional order, cooperating with the United States, and encouraging some Arab accommodation of Israel. So while the leaders of Iran and Saudi Arabia may pay lip service to rejecting sectarian strife and promoting regional coexistence, they view the threats to their interests through entirely different prisms, shaped by opposing ideologies and divergent, if not mutually exclusive, identities. These differences were not resolved in a one-day summit and are unlikely to be resolved in the future unless one of these states is transformed. This was clear in the post-summit "spin" by the two parties. Iranian spokesmen gave enthusiastic accounts of the meeting and focused on the need for Muslim unity; Saudi-oriented media were considerably more reserved and placed the onus for change on Iran because, as one newspaper wrote, "the sense of danger is posed by Iranian conduct in the region and the ensuing American escalation against Iran." Similarly, Iranian spokesmen reacted to a report by the Saudi Press Agency that Iran had endorsed the Saudi peace initiative by claiming that the issue had not been raised in the discussions. These differing interpretations of what took place reflect a more profound contradiction between the two leading Gulf states, which now also embody the two main identity groups in the Islamic world. Indeed, the Iranian-Saudi summit and its murky aftermath encapsulate all the main political trends in the contemporary Middle East. For centuries, the Sunni-Shi'ite fault line ran along the frontier between the Ottoman and Persian Empires. After the collapse of the Ottoman Empire, Iraq (dominated by Sunnis, although the majority of the population was Shi'ite) assumed the role of the Sunni front-line state. As such, Iraq enjoyed the support of most Sunni states, especially Saudi Arabia, during its almost decade-long war against post-revolutionary Iran. Iraq battled Iran to a standstill and preserved the status quo in the 1980s. But after the American-led coalition destroyed Saddam Hussein's regime in 2003, the Sunni-Shi'ite fault line shifted westward into Iraq itself (just as it had shifted eastward two years before into western Afghanistan.) These changes, together with rising Shi'ite self-assertion in Bahrain, Hizbullah's challenge to the Lebanese government, and particularly Iran's undisguised quest for nuclear capability, combined to create a palpable fear throughout the Sunni Arab world of Shi'ite empowerment and Iranian hegemony. King Abdullah of Jordan expressed this fear when he warned about the dangers of a "Shi'ite crescent" in the Levant, and Egyptian President Hosni Mubarak voiced a similar concern when he accused Iraqi Shi'ites of being more loyal to Iran than to their own country. Perhaps the most noteworthy manifestation of this mood came in the summer of 2006, when the Jordanian, Egyptian and Saudi governments reacted to the outbreak of fighting in Lebanon not with ritualistic denunciations of Israel, but rather by criticizing Hizbullah for its irresponsible behavior and, by implication, for acting in the interests of Iran. In another era, Egypt - traditionally the "big brother" of the Arab world - would have taken the lead in responding to the perceived Iranian/Shi'ite challenge. But Egypt is preoccupied with domestic concerns and its declining regional and international influence. That, together with Saudi Arabia's orthodox Sunni centrality, economic clout, and geographic location, have all thrust the latter into a more prominent role. In fact, Saudi Arabia has become the pivotal player in efforts to block the growth of Iranian/Shi'ite power that threatens Sunni interests, American and other Western positions in the region, and Israel. As one defender of Saudi policy put it, "Lebanon cannot be left as a hotbed of political gangs that carry out assassinations and seek to control the country's resources only to thrust the country into the fire of civil war. Riyadh can neither allow Palestine to be a commodity in Iran's hands, nor allow the breeze to blow through Baghdad only from Teheran." These objectives explain Saudi efforts to shore up the Lebanese government, support Sunni and semi-independent Shi'ite factions in Iraq and oppose a premature American withdrawal, and to virtually dictate an agreement on a national unity government for the Palestinian Authority that could potentially extract Hamas from Iran's influence and reduce Arab public sympathy for the Iranian self-proclaimed champions of the Palestinian cause. They even explain the high-level contact with Israel reportedly initiated by such senior Saudi personalities as National Security Adviser Prince Bandar bin Sultan. Saudi Arabia has not been alone in recognizing the primacy of the Iranian/Shi'ite challenge. The United States, which shares the Saudi view, has invested considerable effort in promoting a "coalition of moderate states" to meet that challenge, and since Saudi Arabia and Egypt are critical members of any such coalition, American policymakers have essentially abandoned the campaign for their "democratization" that occupied center stage in the Bush administration's Middle Eastern policy immediately after 9/11. For Israel, Iran and Hizbullah in Lebanon are the most serious threats to its security, and it has adopted a more favorable, though still qualified, attitude to the Saudi peace initiative. While that change in attitude may be enough to maintain communication with Saudi leaders, effective regional and international cooperation against Iran will require more decisive action - if not to resolve the Israeli-Palestinian conflict, then at least to lower its profile in Arab public opinion. The writer is director of research at the Jaffee Center for Strategic Studies, Tel Aviv University.