In 2014, Russia seized the Crimean peninsula and destabilized Ukraine’s Eastern provinces of Donetsk and Luhansk. In the Western world, scholars often interrogate themselves over the possibility to see Crimea returned to Ukraine. Many of them believe that Crimea might not be necessarily lost forever; however, several considerations suggest that the contrary is true. Instead, the case is different for the two provinces in Eastern Ukraine.
To begin with, Russia is installing new missile-defense systems in the peninsula. Back in the spring of 2017, Moscow deployed a division armed with S-400 “Triumph” missile-defense systems near Feodosia, in Crimea. This system is capable of hitting aircrafts and ICBMs flying within a range of 400 km and 60 km respectively. Recently, after the decision of the Trump administration to provide Ukraine with American weapons, Russia responded installing another division of S-400s near the city of Sevastopol. Tellingly, these devices can be turned into “offensive mode” in less than 5 minutes. The symbolic relevance of these moves and the strategic potential of the S-400 clearly indicate that Russia is in Crimea to stay. It is also worth to mention that the only logistic base of Russia’s Black Sea fleet is located in Sevastopol, which thus is an indispensable resource.
Secondly, the seizure of Crimea became a new building block of Russia's national identity. Historically, the political myth of Russia being a strong military power determined the foreign policy of the country and the collective identity of Russian citizens. After the traumatic experience of the fall of the USSR and the 30 years of economic, social and political strife that followed, Crimea represents for Russians the renewed strength of their motherland. This is why giving Crimea back to Ukraine would be a calamity from a Russian standpoint, and imply enormous electoral costs for Vladimir Putin. Also, giving back Crimea would legitimize Ukraine accession to NATO, the same issue that sparked the Crimean crisis.
Regarding the Luhansk and Donetsk provinces, the situation is different. Russia has everything to gain from freezing the status quo. Its aim would be maintaining an area of instability in Ukraine to prevent the country from joining NATO. Should Russia annex the two provinces like it did in Crimea, the remaining part of Ukraine would be free to join the North Atlantic Organization.   Instead, with the two districts under Ukraine's sovereignty but in a situation of frozen conflict, the country would not meet the requirements to join NATO. Moreover, leaving Donetsk and Luhansk under Ukraine’s sovereignty, Russia could still leverage the Russian-speaking population of the two provinces to influence Ukraine’s internal political processes.