The latest developments in Iraq confirm the extent to which the Syrian civil war has broken its banks.Nearly 2,000 people have been killed in sectarian violence in Iraq since April. Many of the fatalities are the result of bombings carried out by the Islamic State of Iraq organization – the Iraqi franchise of al-Qaida.The upturn in violence in Iraq in recent months relates to a number of factors precipitated by events in Syria.Firstly, Iraq’s Sunni population has never willingly accepted the de facto dominance of the country’s Shi’ite population. The Shi’ites constitute the single largest community in the country and as a result, their dominance is largely assured for as long as Iraq holds together and governments are based on a popular mandate.But it is difficult to exaggerate the extent to which Shi’ite rule appears unnatural and unacceptable to Sunnis, who have dominated the Arabic-speaking world for centuries.The new Shi’ite ascendancy was not merely symbolic in nature. Ordinary Iraqi Sunnis have in recent years found themselves facing discrimination on the employment market, in housing, in education and in other areas of life. The government of Prime Minister Nuri al-Maliki, meanwhile, engaged in a triumphalist style. Maliki boasted of crushing the “terrorism” of the Sunni insurgency.Sunni Vice President Tareq al- Hashemi was forced to flee to the autonomous Kurdish north of the country, after being convicted of organizing the murder of political rivals.In recent years, Shi’ite domination appeared to be a fait accompli.No longer. The uprising by Sunni Syrians has served to energize Sunnis in Iraq. As a result, jihadi elements in Iraq evidently consider it an opportune time to recommence operations.Secondly, the border separating Iraq from Syria is poorly maintained. The Iraqi provinces of Anbar and Nineveh – centers of the Sunni insurgency against the Americans after 2003 – abut it. The Sunni tribes on either side of it are closely linked by familial ties. This is ideal ground for fomenting revolt; the transfer of weaponry and men across the border is easily achieved.Sunni jihadi fighters are currently crossing in both directions in increasing numbers. An incident in March in which 51 Syrian soldiers were killed on Iraqi soil was the first indication that the war would cross over with them.Moreover, the Sunnis are responding to a considerable degree to an existing reality in which Iraqi Shi’ites were already engaged in the war in Syria – on the regime’s behalf.Although Prime Minister Maliki officially insists that Iraq is neutral in its neighbor’s war, Baghdad has allowed both its airspace and its territory to be used to transport weapons from Iran to Syria.Iraq is increasingly closely aligned with Iran. In this regard, it is not only Sunnis who are crossing the border to to fight. Growing numbers of Iraqi Shi’ite paramilitaries are doing the same – to engage on behalf of Syrian President Bashar Assad.Members of Muqtada al-Sadr’s Jaish al-Mahdi militia have been observed in recent days making their way into Syria. They join the already active Ahl al-Haq and Kata’ib Hezbollah Iraqi Shi’ite militias in Syria.So what does all this add up to? The emerging reality is one which lays bare the related extreme weakness and questionable future of three states constituting a single, contiguous land area – namely Syria, Lebanon and Iraq. All suffer from the same problem: the existence within their borders of rival sectarian communities with irreconcilable aims. The rival communities, meanwhile, maintain ties of sentiment and organization across the weak and porous state borders.The war in Syria ran along clear sectarian lines from the start – its cradle was in the conservative Sunni region of Deraa, while the armed revolt emerged in the impoverished Sunni rural north.The rebellion was challenging an Iranaligned, non-Sunni elite.The outbreak of sectarian war in the formerly securely Alawite-dominated Syria served to upset the sectarian balance in the two neighboring states. In each of these, as in Syria, the non-Sunnis were dominant in the period prior to the outbreak of the fighting in Syria.In Lebanon, the Iran-aligned Hezbollah movement held the whip hand. In Iraq, the Shi’ite-led government was in the process of moving closer to Tehran.The Syrian revolt established a realistic possibility of a Sunni challenge in both Iraq and Lebanon.Emboldened Sunni radicals are now cooperating across borders. This may be witnessed most clearly in the parallel campaigns of al-Qaida-linked groups – Jabhat al-Nusra in Syria and the Islamic State in Iraq organization.But it is also evident in, for example, the attacks by Syrian rebels on pro- Assad targets – including Hezbollah-dominated south Beirut, the longstanding battles between Assad opponents and loyalists in the northern Lebanese city of Tripoli, and Assad’s air attack this week on the rebel-supporting town of Arsal in Lebanon.So the Sunni revolt in Syria has generated parallel conflicts in Lebanon and Iraq. Indeed, what is happening looks increasingly like a single sectarian war.