Yet another wave of bombings struck Iraq on Monday, killing at least 51 in the latest of the country's worsening violence. The attacks are typically conducted by extremist groups, including al-Qaeda's local branch, who belong to Iraq's Sunni minority, and tend to be committed against civilians from the Shi'a majority. The bombings have long been and continue to be very bad news for Iraqis, who have to worry about terrorism, sectarian violence and the growing threat of political instability.

Iraq's violence is also bad news for Syria. And not just because the group behind many of the bombings, the al-Qaeda-allied ISIS (Islamic State of Iraq and Greater Syria), is also pushing into Syria, where it's importing it's experience at causing mayhem. The stronger that Sunni extremists grow in Iraq, the more that Iraqi leaders are worried about how the war turns out in Syria. They fear that Sunni extremist groups like ISIS will turn all or part of Syria into an al-Qaeda-controlled state, similar to Taliban-run Afghanistan, and use it as a base to launch even more attacks against the Shi'a civilians and government in Iraq.

This fear of an al-Qaeda-run Syria may be leading Iraq's government to offer greater support for Syrian President Bashar al-Assad, whom Baghdad sees as the lesser of two evils. And that support – which also involves Iran – could be playing a significant role in shaping the course of the Syrian civil war.

Iraqi leaders are not in love with Assad and, like American officials, are not eager to get sucked into Syria's civil war. But, according to a recent story by the New Yorker's Dexter Filkins on Iran's regional foreign policy, Iraqi Prime Minister Nouri al-Maliki has chosen to help Assad because he fears what would happen if the Syrian government collapsed. Iraq is not directly involved in Syria, but Maliki does allow Iran to conduct daily flights of personnel and supplies into Syria, where it is playing an increasingly crucial and direct role in propping up Assad.

Here's Filkins explaining why Maliki would allow Iran to help Assad, though he is a friend of neither government and distrusts both. The answer is that he hates Sunni extremists, who are plaguing his country as well as fighting Assad, far more:

So far, Maliki has resisted pressure to supply Assad overland through Iraq. But he hasn't stopped the flights; the prospect of a radical Sunni regime in Syria overcame his reservations about becoming involved in a civil war. "Maliki dislikes the Iranians, and he loathes Assad, but he hates [Syria-based Sunni extremist rebel group] al-Nusra," [former U.S. ambassador to Iraq Ryan] Crocker told me. "He doesn't want an al-Qaeda government in Damascus.

That's something to remember about this part of the Middle East. Sectarian lines don't fall along national borders, which means that turmoil in one country quickly affects another. There's a bit of a feedback loop between Iraq and Syria right now, with violence in one worsening it in the other.

Iraq's instability, a product of the U.S.-led invasion 10 years ago, contributed to the rise of al-Qaeda there. Now those hardened fighters have moved into Syria, making things worse there. Similarly, the civil war in Syria that began as a purely domestic affair has since regionalized; Iraqi leaders are rightly worried they'll be sucked in. So they're helping Assad – or helping Iran help Assad, at least – bolstering him and perpetuating the war, in turn enabling the extremists who feed on chaos. And those extremists, a number of whom came from Iraq, will surely one day come back across.

Around and around the sectarian killing goes, on and on, a vicious cycle by every possible definition.