Although such groups represent a marginal political current, they could have an outsized impact. Iranian and Russian media have covered these incidents extensively in order to feed an anti-NATO slant and increase Ankara's political costs for supporting the Syrian opposition. This narrative could spur further unrest in Turkey, amplifying perceptions of instability.
Southern Turkey's economic integration with Iraq and Syria was one of Ankara's major successes of the past decade. Although the area's overall volume of trade was minor compared to Turkey's overall volume, it was an important factor in the economic development of a long-impoverished portion of the country.
The conflict in Syria has dramatically reversed this trend. As security conditions on the southern frontier deteriorated, Ankara closed the border with Syria to commercial traffic. Meanwhile, Baghdad has periodically blocked trade with Turkey to protest Ankara's rapprochement with the Iraqi Kurds. All of this has meant the closing of previously vibrant trade between southern Turkey and the northern Fertile Crescent. For instance, by November 2012, Hatay's exports to Syria had fallen to less than half their 2010 level, and similar drop-offs have occurred in every southern province (for a chart illustrating these decreases, see the online version of this article).
The resurgence of Kurdistan Workers Party (PKK) violence is the most severe repercussion of Turkey's exposure to the Syrian war. Following Ankara's break with Assad in fall 2011, Damascus abandoned its 1998 commitment to prevent the PKK from operating on its soil. Then as now, Assad had much to gain from fostering the perception that his continued reign was key to limiting the PKK's strength in northern Syria.
Bolstered by this newfound logistical and material support from Syria (and from Assad's patron, Iran), the PKK embarked on a renewed campaign of violence in late 2011 (for a chart illustrating the death toll, see the online version of this article). And in 2012, leader Murat Karayilan announced that the group was shifting from guerrilla warfare to a strategy of seizing territory in pitched battles. The fighting soon escalated into the most intense seen since 1999, when Turkey captured PKK leader Abdullah Ocalan. In one attack late last year, for instance, the group destroyed the sole bridge leading to the small southeastern town of Beytussebap, then cut its electricity and raided the district governor's residence in darkness.
Recent peace talks between Ankara and Ocalan have raised hopes of a ceasefire. Yet the connection between PKK militants in the field and Syrian-Iranian interests is perhaps the most serious obstacle to defusing the violence.
Washington should work closely with Ankara to monitor the many ways in which the Syria conflict is spilling into Turkey. This includes offering closer intelligence cooperation against the PKK and rallying European governments to provide more help as well. Washington should also consider reviving the successful Turkish-Israeli intelligence cooperation against the terrorist group, which stopped following the 2010 Gaza flotilla incident. This could serve as a precursor to normalization of bilateral ties in the aftermath of the Israeli elections. Last but not least, Washington should pay special attention to the rise of extreme-left and nationalist groups in Turkish society, working with Ankara to prevent violence against present and future NATO deployments.