In the past year and a half, Russia has intervened militarily in two countries, Ukraine and Syria, where revolution and extreme political polarization threatened the governments of pro-Russian leaders. And that’s pretty much where the similarities between the campaigns end, except for one other commonality: Both Syria and Ukraine are home to Russian naval bases—in Tartus and Sevastopol, respectively.

Ports, and especially warm-water ports, have long played an important role in Russian foreign policy. Russia isn’t landlocked, of course, but Europe-facing ports such as Arkhangelsk and St. Petersburg were historically ice-locked for part of the year before the advent of the icebreaker in the 20th century (Russia’s port at Murmansk is ice-free, but it was built in 1915, and the Russian port at Vladivostok is on the Pacific). Moreover, none of these ports, even when open for business, allow for easy access to the bustling Mediterranean Sea. This has left Russia with an economic and military incentive to expand toward warmer waters. Beginning just before the reign of Peter the Great in the late 17th century, Russia fought a series of wars with the Ottoman Empire in a quest to establish a warm-water port off the Black Sea. By 1812, Russia had managed to secure control of the entire northern coast of the Black Sea.

Even with year-round ports on the Black Sea, access to the Mediterranean was still governed by the whims of whoever controlled the Dardanelles and Bosporus straits. During World War I, Russia made a never-consummated secret agreement with Britain and France that would have granted it control of Constantinople and the Turkish straits if the Allies proved victorious. Although Russia enjoyed access to naval bases throughout the Mediterranean during the Soviet era, the collapse of the U.S.S.R. brought an end to that access, with the exception of Russia’s base in Tartus, Syria.

Tartus lies on Syria’s western coast and has had a Russian naval presence since 1971. At the time, the Soviet Union was Syria’s primary arms supplier and used the deep-water port as a destination for shipments of Soviet weapons. Russia managed to maintain access to Tartus after the fall of the U.S.S.R. due in part to a deal that wrote off Syrian debts to the Soviet Union. The Russian naval base itself is reportedly less than impressive—it lacks large-scale repair facilities and a command-and-control capability, which would allow Russia to oversee operations from Tartus—but it is able to accommodate all Russian naval vessels except for the Admiral Kuznetsov aircraft carrier, and offers a means of offloading arms and personnel.

The city and naval base of Sevastopol, on the Crimean peninsula, were founded in 1783 by the Russian Empire, and the city remained part of Russia until its transfer to the Ukrainian Soviet Socialist Republic in 1978. Six years after the breakup of the Soviet Union, Russia renounced territorial claims to the city in exchange for a 20-year lease of the warm-water naval base. It’s a military asset with substantial strategic and symbolic value. The base houses Russia’s Black Sea Fleet and Mediterranean Task Force, the latter of which was only reestablished in 2013, and helps Russia project power in the Black Sea region and into the Mediterranean. The port was also the site of two major wartime sieges. As of last year, 15,000 Russian naval personnel were stationed at the base; in 2008, it served as a staging ground for blockades and amphibious landings during Russia’s war with Georgia.

From north to south, the markers point to Sevastopol, the Bosporus, and Tartus. Russia is outside the picture, off to the upper right. (Google Maps)

Jeffrey Mankoff, a Russia expert at the Center for Strategic and International Studies, told me that while Russia’s invasion of Crimea in the spring of 2014, following the revolution that ousted pro-Russian Ukrainian President Viktor Yanukovych, may have occurred regardless, “the presence of the base [at Sevastopol] made doing something there more urgent.” He also noted that Russia chose to go as far as annexing Crimea, thereby ensuring control over Sevastopol, whereas it did not take the same approach in Abkhazia or South Ossetia—two breakaway Georgian republics allied with Russia but not endowed with Russian naval bases.

The base in Tartus may be less valuable than its counterpart in Sevastopol, but the location of the former matters. As the sole Russian naval base beyond the Bosporus—which is controlled by Turkey, a NATO member—Tartus helps establish Russia’s presence in the Mediterranean. “A big part of their continued interest in Syria and in [Syrian President Bashar] Assad has to do with” the Tartus base, Mankoff said. “I think Russia does have a bigger geopolitical view of the world, regards the eastern Mediterranean as an area of importance, and wants to be sure that it can secure its interests there.” According to General Philip Breedlove, NATO’s top commander, Tartus may also be part of a Russian effort to establish an anti-access/area denial (A2/AD) bubble over Syria, designed to prevent NATO forces from taking offensive action against Russia and its allies in the region. As Vice Admiral Viktor Chirkov, the commander in chief of the Russian Navy, succinctly put it, “This base is essential to us.”

Both Sevastopol and Tartus play a role in compensating for Russia’s geographic deficiencies as well. “Russia’s always had the challenge of not having great maritime access, just as a result of its geography, and so to the extent that it wants to be an active player in [the Mediterranean] … it has to have some ability to operate outside of its own coastal waters,” Mankoff explained. This ambition is enshrined in Russia’s new maritime strategy, detailed in the Maritime Doctrine of the Russian Federation 2020. The strategy places particular emphasis on the Atlantic Ocean due to “NATO expansion, the need to integrate Crimea and the Sevastopol naval base into the Russian economy, and to re-establish a permanent Russian Navy presence in the Mediterranean,” according to Russian Deputy Prime Minister Dmitry Rogozin. The doctrine also stresses the importance of the Arctic, given its mineral resources and the easy access it offers to both the Atlantic and Pacific.

All this isn’t to suggest that naval strategy is the primary motivation behind Russia’s interventions to support pro-Russian separatists in Ukraine and Assad in Syria. In the case of Syria, Putin has a track record of opposing Islamist movements like ISIS (in fact, that track record is one of the factors that brought him to power in the first place). Mankoff suggested that Russia’s Syria policy could be a mix of the personal and the political, saying, “If Putin believes that Assad is his guy and that he has a personal obligation to him, then that may play a role above and beyond what the professional diplomats and strategic thinkers believe is going on here.” Additionally, Mankoff argued that the Russian government might be deliberately trying to draw a comparison between its unflinching support of Assad and America’s brittle support of Hosni Mubarak in Egypt, which dissipated during the Arab Spring.

But even if Russia isn’t exclusively mobilizing its military to secure naval bases, the Kremlin has clearly demonstrated that restoring a strong presence on the high seas is a priority. And Vladimir Putin tends to act on his priorities.