When Russia signed the Treaty of Paris in 1856, accepting defeat in the Crimean War—which had decimated its military and ruined its economy—it agreed to dismantle its naval base in the port city of Sevastopol. These were the terms demanded by Britain, France and their allies, who sought to eliminate Russia as a military threat in the Black Sea.

But the concession didn’t last long.

Russia began to rebuild Sevastopol during the Franco-Prussian War, in 1870. And throughout history, Russian leaders would return to Crimea again and again. After Germany’s bombing of Crimea during World War II, much of Sevastopol was in ruins. But Joseph Stalin declared the port a “hero city” and ordered it restored to its former neoclassical beauty.

Indeed, the Crimean peninsula has loomed large for Russian leaders ever since Russian Tsarina Catherine the Great annexed it from the Ottoman Empire in 1783. The strategically located peninsula, which is officially part of Ukraine, has given Russia military leverage not only in the Black Sea, but the greater Mediterranean region. After the fall of the Soviet Union, a 1997 treaty with Ukraine allowed Russia to keep its Black Sea Fleet in Sevastopol, under a lease that has been extended until 2042.

But in 2014, Russia seized Crimea from Ukraine in an illegal move that violated the territorial integrity of the former Soviet republic, and sparked a war that has displaced nearly 2 million people and destroyed the country’s infrastructure. Russian President Vladimir Putin’s justified the aggression, in part, by asserting that Crimea is mostly comprised of ethnic Russians.

For hundreds of years, Crimea has been the home of Tatars, a group of Turkic speakers who lived under the Ottoman Empire until Catherine the Great annexed the region. In 1944, Stalin deported about 200,000 Tatars to Siberia and Central Asia, calling the ethnic Muslims traitors to the USSR and bringing in ethnic Russians to replenish the workforce. After Stalin’s death, Soviet premier Nikita Khrushchev transferred Crimea to Ukraine in a move hailed as a “noble act on behalf of the Russian people.” The transfer was praised at the 1954 meeting of the Presidium of the USSR Soviet Supreme, the Soviet Union’s highest legislative body.

“Comrades…The transfer of the Crimean Oblast (or region) to the Ukrainian SSR is occurring in remarkable days,” said Soviet politician Sharof Rashidov. “This is possible only in our country, where there is no ethnic strife and there are no national differences, where the lives of all the Soviet peoples pass in an atmosphere of peaceful constructive work in the name of the peace and happiness of all humanity…”

“Comrades!…Only in our country is it possible that such a great people as the Russian people magnanimously transferred one of the valuable oblasts to another fraternal people without any hesitation,” said Otto Wille Kuusinen, another Communist Party leader.

But for all the talk about unity and cooperation, recent documents suggest Khrushchev’s move was motivated more by political calculation than goodwill. It was designed to appease Ukrainian leadership and solidify his position in the power struggle that emerged after Stalin’s death in 1953.

Some argue that Putin’s annexation of Crimea is an attempt to return Russia to the glory of its pre-Soviet days, “as one of the world’s greatest civilizations.” Although Ukrainian nationalism remains strong, particularly in the eastern part of the country, Ukrainian officials and analysts report to Radio Free Europe/Radio Liberty that significant demographic transformation is underway, with a huge influx of ethnic Russians.

“We can say with certainty that we are talking about hundreds of thousands of people,” Ukrainian official Borys Babin, told the news service, including many from Siberia. “An enormous number of bureaucrats are moving in with their families, and those family members are looking for work. In addition, there is a large number of guest workers—people who come to Crimea for major construction projects that are being carried out in the military sphere.”

Meanwhile, thousands of Crimean Tatars left the peninsula since the annexation in 2014. The Tatars, many of whom had returned to their ancestral homeland in the 1980s and 1990s, were driven out by an increasingly aggressive Russian presence.

Of those who remain, many are subject to harassment, arrest and imprisonment by Russian authorities, particularly on charges of extremism and political activity, according to a 2017 Human Rights Watch report.