The Black Sea is a crucial theater in the war between Russia and Ukraine.

Russia’s invasion of Ukraine has been fought mostly in a series of grinding land battles, but for the governments in Kyiv and Moscow the Black Sea also has been a vital theater in the war.

Russian warships have in recent months fired a series of cruise missiles at Ukrainian targets that are sometimes hundreds of miles away, hitting towns and cities and damaging the country’s energy infrastructure.

Ukrainian officials regularly warn residents of imminent attacks when they detect the missile carriers in the Black Sea, and the country’s military has made it a strategic priority to pierce Moscow’s aura of naval superiority with a series of bold strikes.

But the importance of the Black Sea — where U.S. officials said an American drone crashed on Tuesday after being struck by a Russian warplane — goes beyond the military contest to the geopolitical and economic interests of Ukraine and Russia. The Black Sea borders both countries — as well as Georgia, Romania, Bulgaria and Turkey — and is a crucial connection between their ports and the Mediterranean Sea.

So critical is the trade route for both countries that it became a rare point of agreement during the war. A deal brokered last July by Turkey and the United Nations established a corridor for ships carrying grain and other food crops to leave Ukrainian ports and pass through a Russian blockade, while also permitting Russia to send through its own shipments of food and fertilizer.

Moscow’s navy has dominated the Black Sea for years, and Russia illegally annexed the Crimean Peninsula in 2014 in part because the city of Sevastopol has for centuries been the home port for its Black Sea fleet. And since last February, Russia has stationed its navy off Ukraine’s coast, effectively blockading Ukraine’s ships in port.

Even as Russia has controlled the waters of the Black Sea, it has been the scene of Ukrainian defiance.

On the first day of the full scale invasion began last February, Ukrainian fighters stationed on Snake Island, a sliver of land off the coast of Odesa, refused to surrender to a Russian naval ship that wanted to take control. That incident came to symbolize Ukraine’s resistance. Russian forces later took over the island but in June they were forced to withdraw after Ukrainian missile strikes.

Some of Ukraine’s most notable attacks have also come in the Black Sea.

A Ukrainian missile strike sank the Moskva, the flagship of Russia’s Black Sea fleet, in April and an explosion badly damaged the Kerch Strait Bridge, which connects Crimea to Russia, in October. The bridge explosion made it harder for Moscow to supply its forces in Crimea and also embarrassed President Vladimir V. Putin of Russia, who had taken personal credit for the bridge’s construction.

Military experts say that Ukraine also used a ship drone to attack the Russian naval fleet off the Crimean port city of Sevastopol in November.

After that attack, Moscow briefly suspended its participation in the grain deal.