Power vacuum lifts militants Gunmen patrol the streets of Fallujah, Iraq. The images of recent days have an eerie familiarity, as if the horrors of the past decade were being played back: masked gunmen recapturing the Iraqi cities of Fallujah and Ramadi. Car bombs exploding amid the elegance of downtown Beirut. Syria's worsening civil war. But for all its echoes, the bloodshed that has engulfed Iraq, Lebanon and Syria in the past two weeks exposes something new: the emergence of a post-American Middle East in which no broker has the power, or will, to contain the region's sectarian hatreds. Behind much of the instability is the bitter rivalry of two great oil powers, Iran and Saudi Arabia, whose rulers - claiming to represent Shiite and Sunni Islam respectively - cynically deploy a sectarian agenda that makes almost any sort of accommodation a heresy. ""I think we are witnessing a turning point, and it could be one of the worst in all our history,"" said Elias Khoury, a Lebanese novelist who lived through his own country's 15-year civil war. ""The West is not there, and we are in the hands of two regional powers, the Saudis and Iranians, each of which is fanatical in its own way. I don't see how they can reach any entente, any rational solution."" The drumbeat of violence in recent weeks threatens to bring back the worst of the Iraqi civil war that the United States touched off with an invasion and then spent billions of dollars and thousands of soldiers" lives to overcome. Linking all this mayhem is an increasingly naked appeal to loyalties of clan and sect. Foreign powers imposing agendas on the region, and the police state tactics of Arab despots, had never allowed communities to work out their relationships openly. These divides have grown steadily more toxic since the Iranian revolution of 1979. The events of recent years have accelerated the trend, as foreign invasions and the recent round of Arab uprisings left the state weak, borders blurred, and people resorting to older loyalties for safety. Arab leaders are moving more aggressively to fill the vacuum left by the US and other Western powers. The Saudi government's pledge last week of $3 billion to the Lebanese army is a strikingly bold bid to reassert influence in a country where Iran has long played a dominant proxy role through Hezbollah, the Shiite movement it finances and arms. That Saudi pledge came just after the assassination of Mohamad Chatah, a prominent political figure allied with the Saudis, in a downtown car bombing that is widely believed to have been the work of the Syrian government or its Iranian or Lebanese allies. Sunni Muslims from Egypt, Libya, Tunisia, Saudi Arabia and elsewhere have joined Syria's rebels. And Shiites from Bahrain, Lebanon, Yemen and even Africa are fighting with pro-government militias, fearing that a defeat for Syrian President Bashar al-Assad would endanger their Shiite brethren everywhere. Some Shiite fighters are trained in Iran or Lebanon before being sent to Syria, and many receive salaries and free room and board, paid for by donations from Shiite communities outside the country. Although the Saudi government waged a bitter struggle with al-Qaeda on its own soil a decade ago, the kingdom now supports Islamist rebels in Syria who often fight alongside al-Qaeda-affiliated groups. The Saudis say they have little choice: Having lobbied unsuccessfully for US intervention in Syria, they believe they must now back whoever can help them defeat Dr Assad's forces and his Iranian allies. For all the attention paid to Syria over the past three years, Iraq's slow disintegration also offers a vivid glimpse of the region's bloody sectarian dynamic. In March 2012, Anthony Blinken, who is now President Barack Obama's deputy national security adviser, gave a speech echoing the White House's rosy view of Iraq's prospects after the withdrawal of US forces. Iraq, Mr Blinken said, was ""less violent, more democratic and more prosperous"" than ""at any time in recent history." But Iraqi Prime Minister Nouri al-Maliki was already pursuing an aggressive campaign against Sunni political figures that infuriated Iraq's Sunni minority. Those sectarian policies gave al-Qaeda in Iraq, which had become a spent force, a golden opportunity to rebuild its reputation as a champion of the Sunnis in Iraq and in neighbouring Syria. Rebranding itself as the Islamic State in Iraq and the Levant (ISIL), the group seized territory in rebel-held parts of Syria, where it now aspires to erase the border between the two countries and carve out a haven for its transnational, jihadist project. As the US rushed weapons to Mr Maliki's government late last year, some analysts said Washington had not pushed the Iraqi prime minister hard enough to be more inclusive. ""Maliki has done everything he could to deepen the sectarian divide over the past year and a half, and he still enjoys unconditional American support,"" said Peter Harling, a senior analyst for the International Crisis Group. ""The pretext is always the same: They don't want to rock the boat. How is this not rocking the boat?"" ""All these countries are suffering the consequences of a state that's no longer sovereign,"" said Paul Salem, vice-president of the Middle East Institute in Washington. ""On the sectarian question, much depends on the Saudi-Iranian rivalry. Will these two powers accommodate each other or continue to wage proxy war?"" For the fighters on the ground, that question comes far too late. ""There is no such thing as coexistence between us and the Sunnis because they are killing my people here and in Lebanon," said Amjad al-Ahmed, a Shiite fighter with a pro-Assad militia in the Syrian city of Homs.