The conflict between Ukraine and Russia has so far been restricted to ground battles over control of eastern Ukraine. Recent developments, however, suggest that the war -- now in its fifth year -- could soon spread to the sea. On Sept. 16, the Ukrainian government announced plans to create a naval base in the Sea of Azov before the end of the year, four days before President Petro Poroshenko confirmed Kiev's intentions in a speech to parliament. The statements come amid military buildups by both Ukraine and Russia in the Sea of Azov, which have been provoked in part by Moscow's construction of a bridge between Crimea and mainland Russia. The bridge has allowed the latter to harass Ukrainian vessels as part of larger restrictions on its shipping. As a result of the growing tensions, a flare-up is now entirely possible on the Sea of Azov, especially if the United...