'In pre-Islamic times, sectarianism was a bipolar struggle between the Christian Byzantine Empire and Zoroastrian Iran, with Iraq often acting as the frontier land between the two superpowers. Over the centuries, powerful Islamic states rose and fell in the Middle East, each embracing a sectarian vision of Islam that would act as an ideological counterweight to that of its foes.
Iraq, proverbially stuck in the middle, was a sectarian trophy to be passed around by the most powerful. Baghdad changed hands no fewer than four times between the Sunni Ottomans and Shia Iran between the years 1508 and 1638, when the city finally came under long-term Sunni domination. This Sunni rule only ended in 2003, when President Bush decided to invade Iraq, starting off the cycle once again.
Today, Sunni-Shia divisions come in the form of a resurgent Iran pitted against a coalition of Sunni-Arab states, namely Saudi Arabia, Jordan and Egypt. Whether or not our leaders articulate it (or even understand it), in the eyes of our Sunni allies America's mission in Iraq has been to uphold a Shia-ruled, Iranian-aligned country with arguably the third largest reserves of oil in the world. To put it simply, many governments in the region would benefit from our mission's failure.
Over the years, thousands upon thousands of Sunni jihadists have streamed into Iraq from places such as Saudi Arabia, Libya, and Egypt. Making up a small minority of the Sunni insurgency, these foreign jihadists are nevertheless responsible for some of the most gruesome acts of violence, mass-casualty events aimed at stoking a chain reaction of sectarianism.'