The Black Sea is not exactly known for its turbulent waters, nor for being a geopolitical flashpoint. This, however, changed quite dramatically in 2014 when Russia annexed Crimea from Ukraine — though the peninsula had originally been gifted to Ukraine by Soviet leader Nikita Khrushchev in 1954. In the meantime, it has developed into a key area of Russian interests on NATO's southeasternmost flank.

Russia is now heavily militarizing Crimea and the Black Sea. Some 28,000 Russian soldiers are stationed on the peninsula. Russia has practically doubled its military budget over the past 10 years. And Ukraine's tiny naval fleet, based along the coast of the Sea of Azov, is under Russian President Vladimir Putin's thumb. Already back in 2008, the Berlin-based German Institute for International and Security Affairs warned that Russia was systematically increasing its military presence in the Black Sea region.

Russia's new submarines and frigates, equipped with long-range Kalibr cruise missiles, pose a serious threat to nearby NATO states, and especially to Bulgaria and Romania.

Read more: What you need to know about the Sea of Azov conflict

Black Sea: Falling under Russian dominance?

In Cold War times, Bulgaria — then a staunch ally of the Soviet Union — and Romania were members of the Warsaw Pact military alliance. Today, however, a new geopolitical situation presents itself, as both Bulgaria and Romania have switched sides and joined NATO. Their Black Sea coasts, meanwhile, are NATO's long-ignored weak spot.

Romania has long warned not to allow Russia to militarily dominate the Black Sea. As such, Bucharest has emphatically urged the deployment of NATO forces in the region, including that of a multinational naval fleet.

Sofia, in turn, rejected calls to deploy NATO forces in the region — after all, Bulgaria still maintains close cultural ties to Russia. This makes Bulgaria NATO's weakest link. Which is compounded by the fact that Sofia relies on Soviet-era military equipment. And Russia knows the various weaknesses of the Soviet air defense systems very well. Yet US President Donald's Trump's insistence that NATO states increase their military spending has not fallen on deaf ears. Bulgarian Prime Minister Boyko Borisov announced in summer 2018 that the country would invest some $2 billion (€2.28 billion) to modernize its armed forces. 

Read more: UN meets after Russia seizes Ukrainian navy ships near Crimea

Russia-Turkey ties too close for NATO's comfort

NATO's Achilles' heel on its southeastern flank looks particularly vulnerable with respect to Turkey. The NATO state has for a long time felt that the West has never seriously deemed it a partner on equal footing. This sense of disappointment is exacerbated by the troubled relationship between Trump and his Turkish counterpart, Recep Tayyip Erdogan. Turkey has long since sought deeper economic and military integration with the East. And has even purchased Russia's S400 missile defense system, to the anger of NATO.

Turkey's naval fleet, and its submarines in particular, are still superior to Russia's armed forces, despite their modernization. But Turkey has adopted a conspicuously neutral stance towards Russia, treating it not as a potential enemy but instead as a prospective partner. This became abundantly clear when Erdogan visited his Russian counterpart Putin after Turkey downed a Russian warplane in Syria. Erdogan apologized for the incident and pledged to pay a generous compensation to the victims. 

Turkey and Russia are not exactly chummy. But long gone are the times when both sides fought wars over the Black Sea region like in the 19th century.

Turkstream

Turkey and Russia pursue shared economic interests with regard to the Black Sea, much to the irritation of NATO and the EU. Last week, Putin and Erdogan agreed that the Turkstream gas pipeline will become operational in late 2019; it will direct gas straight through the Black Sea, bypassing Ukraine. Which means Ukraine will lose out on a sizable chunk of gas transit fees. This, too, is another indication that Russia's economic stranglehold over Ukraine is only increasing.

However, the new pipeline could befit Bulgaria, Serbia, Hungary and Slovakia, as gas would be channeled from Turkey onward towards central Europe as of 2020, though talks are still ongoing. But this fact, too, does not bode well for the security of NATO's southeastern flank.

Read more: Germany offers to mediate between Russia and Ukraine

Ukraine: Isolated and weak

Taken together, all this weakens Ukraine. Yet its president, Petro Poroshenko, will hardly receive more than moral support from the EU and NATO. His wish that NATO dispatch warships to the Crimean peninsula will most likely go unfilled. Ukraine is not part of the military alliance, which is in no hurry to admit the politically volatile country.

As it stands, Ukraine — which remains embroiled in the Donbass fighting and weakened after the annexation of Crimea — is isolated. And while Moscow's annexation and recent actions in the Sea of Azov breached international law, Ukraine lacks the military means to assert its rights.

Power struggle could escalate

The Black Sea region, unlike the Mediterranean or the Baltic region, is no historically and culturally homogeneous area. In Cold War times, the Black Sea marked the southeastern frontier of the Soviet Union. But with Russia, Turkey and the West now vying for influence in the region, a conflict could quickly escalate.  

NATO foreign ministers are set to meet in Brussels on 4 and 5 December — at which time they will certainly discuss the present Black Sea situation. But it is doubtful NATO will opt to permanently increase its naval presence in the region to counter Russia's increasingly assertive stance.