The death of King Abdullah of Saudi Arabia has put the alliance between the largest supplier of oil in the world and the West in the focus once more. With the war with ISIS effectively working to Assad's advantage in Syria, there are voices which now compare Iran more favourably as a force for stability.
There is much to be said for such a view. Attitudes towards Iran have remained hardened as a consequence of Cold War thinking in the 1980s. A primacy was put on the Saudi relationship because it was prepared to back Sunni militant forces against the Soviet Union in Afghanistan and Shi'ite Iran.
Ever since the Syrian Civil War started in 2011, the West's monomaniacal obsession with removing Assad was partly apiece with the old idea that his was a secular 'Arab socialist' dictatorship that had had its day and was backed by an expansionist revolutionary Shi'ite regime in Tehran.
This approach dates back to 1979 when the Soviet Union invaded Afghanistan and when a Western client in the Shah was overthrow. President Carter's administration saw these two events as a direct threat to US predominance in the Persian Gulf and hence the flow of oil to the US.
The Carter Doctrine of 1980 made plain that any threat to the security of America's oil supplies was also simultaneously a threat to its national security which would require the use of force in response. With the end of the Cold War in 1990, the US was drawn in to defeat Saddam's invasion of Kuwait.
To a large extent, Saddam in Iraq has been emboldened to annex Kuwait by the fact he had been backed by the US in an eight year war against Iran ( 1980-1988) and had reason to believe he would get away with a measure that was seen as a threat to Saudi Arabia and Western oil supplies.
Between 1990 and the Second Iraq War of 2003, Saddam's ailing dictatorship preserved the balance of forces within Iraq between Sunni and Shi'ite Arabs at an appalling cost to the people in Iraq. However, it forestalled any geopolitical clash between Saudi Arabia and Iran.
The US invasion was intended to reduce US oil dependency on a Saudi Arabia that was increasingly unstable and diverting discontent outwards through funding of Sunni militant causes and to trigger off a 'democratic revolution' throughout the Middle East from the Eastern Mediterranean to the Gulf.
The invasion of Iraq was meant to roll out and unfurl a democratic revolution that started with the collapse of the Soviet Union and liberation of Eastern Europe and Central Asia into a region where old style totalitarian secular regimes still prevailed along with their theocratic version in Tehran.
What it achieved instead was a chaotic and bloody sectarian war with the Shi'ite militias backed by Iran gaining ascendency over the Sunni Arabs who accounted for 20% of the population and had been dominant under Saddam. The Kurdish region developed its oil resources and political autonomy
By 2007, the price of a temporary stability had been bought at the cost of bribing Sunni leaders while acquiescing in the ethnic-sectarian cleansing of Sunnis by Shi'ite militias. This caused a long standing resentment that surfaced again when Sunni Arab aligned with ISIS after its 2014 incursion into Iraq.
The renewed instability in Iraq was a knock on effect of the Syrian conflict. The strategy by 2012 was for the West to back Turkey's attempt to assert its regional influence in Syria as a 'moderate' Sunni Islamist and democratic power along with Qatari financial assistance there and in Egypt and Yemen.
The backing given to the Free Syria Army backfired as Saudi Arabia and Qatar got involved in a race to try and back to most effective Sunni militants on the ground in rivalry with each other and in opposition to Iran which backed not only Assad but also Hizbollah in neighbouring Lebanon.
Division among the Sunni powers reflected different geopolitical agendas. The Saudis had no interest in the grand strategy of removing Assad the better to advance Qatar's plan to build a gas pipeline from the Persian Gulf through Syria to the Eastern Mediterranean. Iran planned a rival pipeline.
By late 2014-2015 it was clear that the states created in 1920 by Britain and France of out the remnants of the Ottoman Empire-Syria and Iraq-could cease to exist. ISIS made a point of erasing the hated Sykes-Picot border drawn up in 1916, one seen as humiliating Sunni Arab Muslims.
So, in actual fact, what has happened in the post-Cold War World is the gradual re-emergence of regional powers with aspirations not unlike the former empires of which Turkey and Iran were once the central, predominant and core part-the Ottoman and Persian Empires.
With the collapse and fragmentation of Iraq and Syria along ethnic-sectarian fissure lines, Turkey and Qatar along with Saudi Arabia and Iran have been vying for power political influence and trying to back military forces that would steer the outcome of these conflicts towards their advantage.
The decision to engage more with Iran diplomatically aims at reducing the possibility of it pursuing a nuclear weapon programme and as part of a region wide effort to lesson tensions from Iraq to Syria to Yemen. This has become ever more vital as Shi'ite forces appear to be gaining ground
The Turkish-Qatari strategy of bolstering Sunni democratic forces in the Middle East by 2013-14 had failed. The Free Syria Army was reduced to a small negligible force with ISIS prevailing. the Muslim Brotherhood was banned in Egypt with a full scale war against insurgent forces raging in Sinai.
While proxy war between Qatar, a loose canon in Middle East, and the other Gulf states continues in Libya, to the east from Lebanon through Syria and Iraq down to Bahrain and Saudi Arabia, sectarian clashes are a consequence of a lethal proxy war between the Sunni Gulf states and Shi'ite Iran.
The US and the Western powers have managed to form a coalition that unites the Sunni Gulf states and has in common with Iran the quest to beat back ISIS and the threat that it would pose, had it been left unchecked, to the present and future stabilities of global oil supplies.
The US has dramatically reduced its supply of oil from Saudi Arabia since the 'shale oil revolution'. This has increased the freedom to use the global oil glut and falling prices as a weapon with which Washington can reconfigure global power politics in tandem with imposing punitive sanctions.
Iran and Russia have been the main targets of this economic warfare because of America and its allies having their own geopolitical strategies to advance control over global energy flows thwarted by them both in Syria and Ukraine respectively. The only real beneficiary of this has been China.
China had much to gain from Russia turning to it in order to make up for lost revenues caused by sanction by striking new gas deals. China also is close to Tehran because of increased supplies of oil. So it is unlikely that the US is going to move away from the alliance with Saudi Arabia entirely.
Washington would prefer a lessening of the proxy war between the Saudis and Iran as it seeks to redirect its diplomatic focus towards East Asia. In Syria, the strategy of removing Assad was effectively admitted to be a failure in the new year of 2015 when the US started indicating it was ready to deal with Assad.
Assad not only failed 'to go': the huge amount of finance from Saudi Arabia and Qatar in bankrolling Sunni militant groups only ended up benefitting and emboldening ISIS both materially and through constant defections to ISIS from other jihadi insurgents. Washington is realising Assad has to be part of the solution.
None of this means the US could simply 'disengage' with Saudi Arabia and realign with Iran. What is being attempted is a balancing act so that both regional powers are involved in defeating ISIS and hence forestalling any threat to global oil supplies and the recovery of the Western economies after the crash of 2008.
The US could not disengage with Saudi Arabia.Even if it has reduced its oil dependence, China has not. 20% of China's oil imports come from Saudi Arabia . The relatively cheap cost of the consumer goods Western citizens expect to be able to buy would end if Saudi oil supplies were threatened.
Moreover, China is making inroads into both Saudi Arabia and Iran; neither would need to do what the US insists it should if China could step in to assist with arms deals with Riyadh and in nuclear technology for Tehran. China has been courting both Egypt and the Saudis so as to sell its weapons
Historically, the US could count on Saudi Arabia as an ally. However, in recent years, especially after the 2010-11 decision to disengage from the level of direct military involvement seen in the Bush years, Arabia is not dependent on the US and could pivot towards China if it were displeased.