ISTANBUL — If you had to rank the spots around the globe where the militaries of the United States and Russia could physically run into each other, the Black Sea would probably be near the top of the list.
The giant body of water on Europe’s southeastern flank has long been a theater of international competition between the United States and its European allies on one side and Russia and its sphere of influence on the other, a dynamic that has been supercharged by Russia’s invasion of Ukraine.
The Russian air force’s downing of an American surveillance drone on Tuesday served as a stark reminder to the many countries operating in and around the Black Sea of the region’s potential to become a flash point, accidentally or otherwise.
“It has always been complicated, it remains complicated, but the stakes are much higher now,” said Ian Lesser, the vice president of the German Marshall Fund of the United States, a research group. “And the longer the conflict goes on, the higher the risks of things spinning out of control.”
The Black Sea is larger than California, with six countries on its coast. Three of those countries, Turkey, Romania and Bulgaria, are members of NATO, while others, like Ukraine, are friendly to the alliance, which has long considered the Black Sea essential to its efforts to contain Russia.
Turkey has tremendous influence over the Black Sea since it controls two straits, the Dardanelles and the Bosporus, which ships must pass through to transit between the Black Sea and other global water ways. The Montreux Convention of 1936 gives Turkey the right to close the straits to most military traffic in times of war, a power it exercised after Russia invaded Ukraine last year.
The Black Sea is hugely important to the efforts of President Vladimir V. Putin of Russia to expand Moscow’s influence and, stemming from that, it has been a locus of instability. The surrounding region in recent years has seen Russia’s war with Georgia in 2008, political uprisings against Russian-backed leaders in Ukraine and Belarus and a war between Azerbaijan and Armenia in 2020, eventually mediated by Moscow.
The State of the War
But Mr. Putin’s biggest power play around the Black Sea was the occupation of Crimea, a strategic peninsula that Russia seized from neighboring Ukraine in 2014. That enhanced Russia’s position in the Black Sea and gave it control of Sevastopol, Russia’s only warm water port.
In the years since, Mr. Putin has increased Russia’s naval presence in the Black Sea, so much so that in 2016, President Recep Tayyip Erdogan of Turkey warned that the sea had “almost become a Russian lake.”
Russia’s foes responded by intensifying their own military maneuvers around the Black Sea. NATO members flew regular surveillance flights and the United States and Britain often dispatched warships, although international conventions kept them from remaining longer than 21 days.
Then Russia invaded Ukraine, causing both sides to further expand their maneuvers in the area.
“The tensions in the Black Sea were obviously amplified after the war,” said Arda Mevlutoglu, an independent Turkish defense analyst.
The war complicated maritime trade for Black Sea nations, and Russia initially blocked the export of grain from Ukraine, one of the world’s top producers, raising fears of an exacerbated hunger crisis in poor nations.
But Turkey helped broker an agreement overseen by the United Nations that has facilitated the export of more than 22 million metric tons of that grain through Turkey’s territorial waters.
Turkey’s closure of the straits to most military traffic, which was meant to prevent Russia from bolstering its naval force against Ukraine with ships from elsewhere, also kept ships from the United States and other NATO nations from entering the Black Sea.
At present, only countries with Black Sea coastlines have vessels in the water, said Yoruk Isik, a nonresident scholar at the Middle East Institute who closely monitors marine traffic through Turkey’s straits.
Of those, only Russia and Turkey have powerful navies, Mr. Isik said. Romania and Bulgaria have smaller forces, Georgia has only a coast guard and the movements of Ukrainian vessels are complicated by the war.
But the skies remain open, so NATO members have increased surveillance flights over and around the sea and Russia has responded with fighter jets as a show of force.
The Pentagon said that the drone that came down on Tuesday was unarmed and had taken off from Romania for a routine surveillance flight. About 75 miles south of Crimea, two Russian fighter jets intercepted it, dumping fuel on it, presumably to blur its camera. The jets also flew close to the drone in a way that U.S. officials described as dangerous.
One of the jets clipped the drone’s propeller, causing its American operators to bring it down, the Pentagon said.
The Russian Defense Ministry told a different story, saying in a statement that the Russian Air Force had scrambled fighter jets to identify the drone, which then maneuvered sharply, lost altitude and hit the water.
United States officials had worried in recent months that some sort of incident over the Black Sea, even an accidental collision or miscommunication, could spiral out of control.
The downing of the drone has heightened tensions between the United States and Russia, although neither side has shown any inclination to allow the situation to escalate.
But analysts said that the war in Ukraine had led to so much more military activity in and around the Black Sea and elsewhere that the longer it lasts, the greater the chances that such incidents will occur.
“It simply points out that the potential geography of confrontation and escalation is much broader than what one may assume by reading the daily news,” said Mr. Lesser of the German Marshall Fund.
Ben Hubbard and Gulsin Harman reported from Istanbul.