Here's Why Shutting the Turkish Border With the Islamic State Is Easier Said Than Done

President Barack Obama just told the Turks that they need to get their act together and stop the massive flow of people, money, and supplies trying to get into Syria, and the oil, artifacts, and more people trying to get out. But if we know this is how the Islamic State (IS) gets supplied, why hasn't someone already shut down the main supply route the group has been using since its emergence?

The "Why now?" question has a fairly straightforward answer. For starters, we've now had both the Turkish shootdown of a Russian fighter jet and, more significantly, the big terrorist attacks in Paris. Russian media has gone completely nuts about the shootdown, publishing in a barrage of negative stories, including accusations (or at least insinuations) that Turkey is tacitly supporting IS. And strictly speaking, from a very specific point of view, the Russians have a legitimate grievance about Turkey not going out of its way to fight the Islamic State. Beyond that, however, the attacks in Paris have put a lot of folks on notice that they need to step up their game regarding IS. So Turkey has been lagging on its anti-IS efforts, for example by not controlling the border, and people are getting increasingly impatient with anyone thought to be playing footsie with the Islamic State.

Related: Why The Hell Did Turkey Shoot Down a Russian Fighter Jet?

That might be an issue right now, but it still doesn't answer the question of why nobody has shut the front door on IS. From one perspective, it's gotten easier and easier to do this. Although Syria's longest land border is with Turkey and runs some 500 miles, the Turks aren't being pressured to secure the whole thing. Most of the territory near the border on the Syrian side is already in a buffer zone some 25 to 50 miles deep and under Kurdish control.

The Kurds probably won't be able to extend their control over the entire border area because the population mostly isn't Kurdish, but rather Syrian Turkmen, who are essentially ethnic Turks living in Syria who don't actually speak Turkish. (The Assad regime forbade them from doing so.) The Syrian Turkmen are being supported, with varying degrees of obviousness, by the Turkish government as an anti-Assad, anti-IS movement with close links to the Free Syrian Army (aka FSA, or the "good" Syrian rebels). Now, there are some border regions that are both populated by Syrian Turkmen and under control of the FSA, but those stretches aren't much of an issue.

Watch the VICE News documentary British Jihadists in Syria:

What's left is a 60-mile-wide swath where IS-controlled territory runs right up to the border. This area is heavily populated by Syrian Turkmen. Now, the interesting bit is that this is the same area that the US and Turkey talked about establishing as a sort of safe zone. The idea is that the US and its coalition buddies would partner up to provide the air portion of a campaign, and the rebels, very Turkish rebels in this case, would take the ground and carve out their own turf, just like the Kurds have done along much of the rest of the border.

But nothing has come of this idea. Barin Kayaoglu, a US-based analyst who specializes in Turkish politics, explained that "their 'safe zone' idea is deader than ever, but that doesn't mean Ankara will stop supporting Turkmen factions of the FSA — or the FSA more broadly."

Thus, the first problem with completely and absolutely shutting down the border is that it would mean the Turks would have to substantially dial back their engagement with the "good" Syrian rebels, assuming it were even possible to seal the border.

Current plans call for as many as 30,000 troops to cover the entire stretch. That works out to a guy about every 10.5 feet or so (or about three and a quarter meters for those counting in metric). Obviously there won't be a line of soldiers from one end to the other.

Related: Dozens Killed In Bomb Attack On Turkish Border Town

In practice, "sealing the border means controlling checkpoints," explained Anthony Cordesman of the Washington-based Center for Strategic and International Studies, "and you can deal with infiltration [through] scouting and patrolling."

The bigger problem is that the very porous border has been a smuggling route for decades, and that's a very lucrative business. Sneaking oil across the line in contravention of bans and restrictions has been a regional pastime since Saddam Hussein first pissed off the United Nations back in 1991. IS didn't invent smuggling across that border, it just changed the name on the "accounts payable" line.

"Certainly Turkey could do more, and putting forces in the area would have a significant deterrent effect," Cordesman said. "But you can't just build a wall and declare it sealed." Beyond that, it's not like everyone doing business across the border is proudly wearing an "Islamic State and Lovin' It" button. There's a whole slew of middlemen and handoffs and cutouts that crop up in a well-developed smuggling economy, and this is no different.

In the end, Turkey can — and probably will — move some folks around and make a big production out of it, but nobody should expect the border to become hermetically sealed overnight. Even the least friendly border in the world, between South and North Korea, still sees people occasionally sneak across to defect. Even creating a mini-buffer state between Turkey and Syria — effectively creating another set of borders — won't be enough to withstand the osmotic pressure of all that money and all those people who are keen to avoid going through proper channels.

Follow Ryan Faith on Twitter: @Operation_Ryan