Earlier this week on these very pages I warned about the rise of violent Islamist extremism, not exclusively but especially in Syria. Unfortunately, in just a few short days, the situation has gotten worse.

I’m thinking about Iraq.

On Tuesday, Iraq’s second-largest city, Mosul, was overrun by an al-Qaeda “offshoot,” the Islamic State of Iraq and Syria, or ISIS — a hellish terror group bent on establishing a regional Islamist state.

Considering its success already in taking — and holding — territory in Syria and now in Iraq, ISIS is making real progress on doing just that.

Indeed, Iraqi Prime Minister Nouri al-Maliki called for a state of emergency as news of Iraqi police and army desertions, jail breaks, the capture of government buildings, military bases and weapons, TV stations, and the airport roll in.

With Baghdad possibly the next strategic objective for ISIS and a sectarian civil war in the offing, cries from Iraq for international assistance are ringing out.

It’s understandable: Iraq has been battling a terrorist/militant insurgency in the country’s western Anbar province, including an ongoing battle for Fallujah, a city not far from Baghdad.

News reports assert that along with Mosul as many as one million people have been displaced this year due to fighting with terrorist and militant groups across Iraq; 800 people were killed in May alone, making it the deadliest month this year. (Some believe the number is much higher.)

The United Nations estimate of 9,000 lives lost last year made 2013 the bloodiest year in Iraq since the height of the insurgency (circa 2006-2007) before the U.S. troop “surge” collapsed al-Qaeda in Iraq (which later morphed into ISIS), bringing stability to the country.

Unfortunately, it appears the gains achieved by the surge have been lost — at least for the moment. But how?

While the al-Maliki government must take the bulk of the blame for the chaos, the complete U.S. withdrawal from Iraq in 2011 is increasingly looking like a major foreign policy/national security blunder.

Though a security transition from U.S. to Iraqi forces was needed, the failure to engage and assist Iraqi forces after the pull-out with key issues — like military training, advice and intelligence — helped lead us to where we are today.

The unraveling Syrian situation and our inattention to it haven’t helped, either. ISIS holds a swath of territory on both sides of the Iraq-Syria border, serving as a safe haven for terror operations into both countries.

While there’s no shortage of hand-wringing and heartache over our Iraq experience, we still have national interests there, such as battling violent Islamist extremism, the security of regional allies and friends, human rights and liberties, and global energy supplies.

The inconvenient fact is that the instability in Iraq and Syria are feeding off one another — and while already affecting neighboring states may spread in a more significant way.

It also serves as a cautionary tale for Afghanistan.

As such, now would be a good time for an effective plan for dealing with this growing threat to U.S. interests and security. Regrettably, it’s not clear we have one.

 - Peter Brookes is a Heritage Foundation senior fellow and a former deputy assistant secretary of defense.