War in Iraq is in the news again, although minus the definite article.

This isn’t “the war in Iraq;” i.e., our war there, George W. Bush’s disastrous military adventure that started in 2003 and ended, at least officially, in December of 2011, having cost nearly 5000 American lives, perhaps as many as 500,000 Iraqi lives, and more than a trillion taxpayer dollars.

What’s happening these days in Iraq is the work of men in sneakers and black masks toting Russian-made weapons. The writing on the flags the combatants wave, either in triumph at the taking of an oil field or in tearful rage at the funeral of a car-bombing victim, is Arabic script. The violence is, in the main, Muslim on Muslim, although the religious minorities in the region — including a small Christian community — have suffered gravely.

The recent civil war in Syria, which involved a bewildering array of factions, all fighting among themselves as they sought to oust President al-Bashir, never really gained traction with the American public. We paid attention when we learned that al-Bashir was using chemical weapons against civilians, a war crime that was not only news-worthy, but had serious implications for our own fighting forces. But aside from that, there was little appetite for American engagement in yet another bloody sectarian conflict.

But as our attention turned to other matters, the war churned on, creating winners and losers. One of the big winners was a group known as ISIS, an acronym for the “Islamic State of Iraq and Syria.”

ISIS fighters were problematic rebels from the get-go. Syria has a long history as an international crossroads; over the centuries, one of its hallmarks has been religious tolerance and plurality. The ISIS fighters, on the other hand, are strict jihadists, believers in the most austere form of Islam, and enforcers of strict shari’ah law — in other words, fundamentalists, many of them foreigners, in the mode of Al Qaeda.

The goals of the ISIS leadership were at odds with the other Syrian rebels, who saw the ouster of al-Bashir as their first, and most important, piece of business. The other rebels watched, astonished, as ISIS fighters sometimes refused to engage with al-Bashir’s forces, on the grounds that the war was about something much larger than a coup, much larger, in fact, than the future of Syria. What ISIS wanted was nothing less than the creation of a new caliphate that would erase the border between Syria and Iraq, and unite areas in both countries dominated by Sunnis.

You may ask: what, exactly, is a caliphate? And why would anyone want to establish a modern one?

The Western sense of linear history collapses as soon as you start to chase the meaning of a word like “caliphate,” which has its origins in the succession crisis that followed the death of Prophet Mohammed in 632. The decades after Mohammed’s death saw a incredibly rapid military expansion of the Islamist empire, but also ferocious infighting among the leadership for the title of “rightful successor” to the Prophet.

In fact, the word “caliph” is derived from the Arabic khalifa, which can be directly translated as “successor.” A caliph is not only a political leader; he is also the supreme religious authority. But in a religion like Islam, there’s a built-in dynastic problem: the caliph is essentially standing in for the Prophet. But how is an ordinary man to do that?

Between the years 632 and 661, there were four caliphs. The fourth was known as “Ali,” an abbreviation of a much longer name. Sunni Muslims believe that these four caliphs were all rightful successors to the Prophet; Shia Muslims believe that the first three caliphs were illegitimate. In the Shia worldview, Ali was the first true successor to the Prophet.

It’s worth noting that Ali’s reign, from 656 to 661, corresponded to the first civil war within Islam, known as the fitna. Sunnis and Shia have been fighting over Ali’s legacy ever since. The Iraq of 2014 is merely the latest battlefield in a war that has been raging, on and off, for more than thirteen centuries.

What, then, is our responsibility to the more or less secular government of Iraq, which has already begun calling for American involvement in the form of airstrikes to help stem the ISIS incursion? There’s a great temptation to say to the Iraqis, “We have done enough. More than enough. This is a regional problem — a problem for Islam to solve.”

Unfortunately, it’s not in our national interest to allow ISIS, and, by extension, Al Qaeda, to create a petroleum-enriched terrorist state in the region.

I’m afraid we may soon find ourselves once again locking horns with 7th century politicians armed with 21st century hardware.