Two notable developments occurred Nov. 11 related to Europe’s migrant crisis, notable not so much for what they directly achieved but for their potential effects. Both events concerned the migration route that passes across the eastern Mediterranean and up through the Balkans, which has been largely responsible for the massive uptick in immigrant numbers in 2015. The first was a statement from the Czech Republic’s deputy prime minister, Andrej Babis, who said that since Greece has not been adequately controlling its borders it should be ejected from the Schengen zone, which allows free movement of people in Europe. The second was the news that Slovenia has begun to erect a fence on its border with Croatia.

Babis’ comments are important: Greece’s exclusion from the Schengen area would deal a blow both to the European Union itself and to Greece’s place within it. The links among its members have already been strained by the immigrant crisis, with some countries claiming emergency conditions and erecting fences with their non-Schengen neighbors, while others have suspended border crossings within the borderless zone, temporarily nullifying its effects. If a country were to be booted out of the borderless area, it would be a further blow to the structural integrity of the entire initiative. For Greece, meanwhile, whose continued existence in the European Union has been in doubt for much of the year primarily for financial reasons, would see another rope that ties it to the union severed, creating even more distance between Greeks and their European counterparts and thus facilitating an eventual Grexit.

Potentially consequential though Babis’ statements may be, Greece is probably not leaving the Schengen area any time soon. Europe’s leaders will be well aware of the risks its departure creates, and kicking Greece out would not actually help the situation that much. This is because Schengen is a system designed to make it easy to cross the borders that exist between Schengen members, removing the need for papers to be checked. Greece’s Schengen membership is not a factor in the current crisis because Greece does not have any Schengen neighbors, so any migrants traveling by land are entering the Schengen area when they enter Greece, but they then leave it again to continue up through the Balkans before entering it once more in countries such as Hungary or Slovenia. If migrants were entering Greece and at that stage booking flights or ferries to other Schengen territories, it might be an issue. But at this stage they are not (at least not in significant numbers).

It is the second development that actually has the potential to change the situation on the ground more dramatically. Slovenia has said it is building a fence to control the flow of migrants — not to cut off that flow — but once the building has begun it is not hard to imagine it continuing to its natural conclusion. This would close off the narrow passage through which the migrants currently pass. Throughout the year, migrants have taken small boats from Turkey to Greek islands, ridden to the mainland by ferry, and made their way up through Macedonia and Serbia to Europe. Hungary’s erection of fences on its border first with Serbia and then with Croatia has steadily driven the flow westward, until the majority of the migrants have been passing through the bottleneck of the Croatia-Slovenia border. This has created so many problems in Slovenia that they have decided to erect a fence to inhibit migrants. If the fence did end up passing all the way from the Hungarian border to the Adriatic Sea, it would finally plug the migrants’ route, since there would be no way to continue going west — at least not by land.

Under such circumstances, the migrants, whose flow to Europe has thus far not abated in November, would be facing some hard choices. If they decided to take their chances on an eastern land route up through Romania, there would be a high likelihood that Hungary would soon erect a fence on that border as well, just as it did on its border with Serbia and Croatia earlier in the year. At that stage, the migrants might continue northward, assuming they could overcome the barrier of the Carpathian Mountains, and into Ukraine, which is not currently the most hospitable of states, and on to Slovakia and Poland, which are themselves two of the more anti-migrant countries.

Alternatively, migrants might start to seek different routes to Europe, routes that would probably require another sea crossing into Italy, most easily at the top of the peninsula between Croatia and Trieste. If that were inhibited by Croatian and Italian authorities, migrants would have to attempt a longer crossing farther down the Adriatic Sea. This would be similar (though in most cases longer) to the crossing they would have made from Turkey to Greece, though it is unlikely that they would be able to find transport so easily. After a year of building migrant flows there is now a small cottage industry operating off the Turkish coast that provides inflatable boats for the quantities of people making the crossing every day, but even this very mobile and opportunistic industry would take a while to get going on the Dalmatian coast. The high numbers of migrants butting up against the new Slovenian fence would be unlikely to be able to find an accommodating group of black market traffickers able to provide vessels for so many customers at such short notice.

Thus, faced with these two unattractive options, there is a high possibility that many of these migrants would find themselves stuck on the wrong side of the European fences for an extended period. This would have the potential to be very destructive. The Balkan states, which would then have to cope with large numbers of people not just passing through but actually remaining, have already exchanged angry words this year. For a multitude of ethnic and historical reasons the region has a reputation for being a powder keg, and throwing in the spark of having to support large numbers of migrants who cannot go forward and cannot go back could have serious consequences. Added to the regional tensions there is also the possibility of a humanitarian crisis as winter draws in, and these countries are some of the least prepared in Europe to be able to provide extensive facilities for these people. Slovenia, then, constitutes an ever-narrowing bottleneck through which the flow of migrants is still being allowed to pass. The consequences of shutting this bottleneck, if it were to happen, could be disastrous for the region and for Europe as a whole.

Republished courtesy of Stratfor