Three Ukrainian naval ships, which were seized by Russian forces, were anchored in a port in Kerch, Crimea, in November. (Alla Dmitrieva/Reuters)
By Sara McLaughlin Mitchell
Russia and Ukraine have been fighting for several years on land, but the two clashed at sea recently. How likely is this maritime conflict to escalate?
Maritime disputes feature prominently in global politics. China’s maritime conflicts with neighboring states over the Senkaku/Diaoyu, Spratly, Paracels and other small islands and reefs have generated over a dozen militarized clashes at sea since 1991. Confrontations in the Kerch Strait between Russia and Ukraine on Nov. 25 and the imposition of limited martial law in Ukraine create similar concerns about escalation of the situation to war.
[Why did Ukraine impose martial law?]
There are several diplomatic issues at stake in the Russia-Ukraine relationship, and understanding these points of contention can help clarify the escalation risks. Our research shows that maritime disputes connected to territorial and identity issues face higher risks of war.
How we did our research
For nearly 20 years, I have worked with Paul Hensel on the Issue Correlates of War (ICOW) project to understand the issues that countries dispute diplomatically, including land borders/islands, maritime areas, cross-border rivers and identity issues.
Scholars have studied the diplomatic issues at stake in interstate crises and wars, discovering that countries tend to fight most wars over territory. Yet we miss cases where diplomatic conflicts arise, but no militarization occurs — this accounts for more than half of all border disputes.
The ICOW project captures these successful cases of peaceful diplomacy by identifying potential situations where countries could have diplomatic disagreement over an issue, and then using media and historical sources to code cases that occurred. Two countries that share a contiguous land border, maritime space or ethnic group, such as Russia and Ukraine, become a pair of countries that could experience an issue claim in our data set.
[Russia and Ukraine had a short naval battle. Here’s what you need to know.]
Using this approach, we identified 843 territorial claims between pairs of countries (1816-2001) and 270 maritime and 143 river claims (1900-2001). In collaboration with Andrew Owsiak and Krista Wiegand, ICOW also collects data on identity claims, coding 157 identity claims between bordering countries since 1946. Russia’s attempt to influence the treatment of ethnic Russians in Ukraine falls into this category.
Issue claims increasingly play out at sea, not on land
Russia’s 2014 annexation of the Crimean Peninsula from Ukraine is an interesting case for many reasons. It’s the first successful territorial conquest since the 1970s in an era of declining territorial disputes. As territorial integrity norms increased, countries shifted from territorial conquest attempts to claims in maritime and identity arenas. For example, beyond Crimea, Russia has not utilized a strategy of territorial conquest to support all ethnic Russians living in Ukraine, but rather limited its support to secessionist movements in Eastern Ukraine.
Meanwhile, maritime conflicts between countries have increased globally since World War II. The Kerch Strait conflict illustrates how unsettled maritime disputes increase the risks for territorial and identity issues to emerge — and for multi-issue conflicts to escalate to violence.
Why have Russia and Ukraine disagreed about their maritime boundaries? 
What exactly are Russia and Ukraine fighting about?
In 1997, Russia and Ukraine signed a treaty demarcating land and maritime boundaries and dividing naval ships in the Black Sea Fleet. However, the countries disagreed on delimitation of the maritime border in the Sea of Azov.
The maritime dispute involves multiple points of disagreement. While the two sides agreed in 1996 that the Sea of Azov is an internal sea, they disagreed about how to divide zones of maritime sovereignty. Russia wanted a seabed boundary for mineral resources, but shared use of water and biological resources. Ukraine wanted the maritime boundary to be drawn along the surface, giving it 60 percent of the area.
Maritime tensions escalated in 2003 when Russia sought to build an artificial isthmus between the Ukrainian island of Tuzla in the Kerch Strait and the Russian Taman Peninsula. And though the two sides resolved disagreements about control of the Sevastopol naval base, conflicts escalated further in 2005 when Gazprom increased natural gas prices for Ukraine — and Ukraine retaliated by increasing rental costs charged to Moscow for the naval base.
While the two sides have signed several agreements over maritime delimitation in the past 15 years, completion of the Kerch bridge in May, Russia’s ramped-up searches of vessels in the strait and disagreements about movements of naval vessels in the area set the stage for the 2018 clash.
How likely is war in the future? 
What makes this maritime conflict particularly dangerous is that it has so many dimensions — it’s not just about the sea. 
Russia and Ukraine are competing over multiple diplomatic issues. This includes a maritime claim involving demarcation of the Sea of Azov (since 1993), a territorial claim by Ukraine protesting Russia’s control of Crimea (since 2014) and an identity claim by Russia protesting the treatment of ethnic Russians in Ukraine (since 1991). ICOW research shows that multi-issue conflicts are more likely to be militarized. While Russia and Ukraine demarcated the land border early in Ukraine’s post-independence period, ongoing disagreements over maritime boundaries in the Sea of Azov and Kerch Strait fueled the emergence of territorial and ethnic identity claims.
The risk of war is also high because contested maritime issues are now connected to territorial claims over Crimea, the most militarized issue in the ICOW data. The importance of Sevastopol for the Black Sea Fleet, combined with the fear of NATO vessels operating in the area, boosted Russia’s claims to Crimean territory.
Of the 270 maritime claims in our data set, close to one-third involve at least one militarized dispute. Risks for violence are higher for cases that also involve disputes over ownership of territory (e.g., Falkland Islands or Senkaku/Diaoyu Islands). Militarized disputes in 2005 and 2008 set the stage for Russia’s grab for Crimea and construction of the bridge across the Kerch Strait, crippling Ukraine’s naval capabilities. Highly salient diplomatic issues with a history of militarized conflict carry higher risks for escalation to war.
Some factors may push toward a peaceful resolution, including Russia’s capability advantage over Ukraine and verbal support of Ukraine by NATO and E.U. member states. Yet ICOW research shows that conflict risks in this area will remain high. Our work suggests maritime claims create risky security environments when linked to territorial claims and a history of militarization.
Sara McLaughlin Mitchell is the F. Wendell Miller Professor of Political Science at the University of Iowa and author of five books and more than 40 journal articles and book chapters. Follow her on Twitter at @sbmitche.