Russia’s extreme suspicion of what happened in Ukraine spurred them to take back the Crimea as soon as late February 2014, barely a month after Yanukovych was forced to flee government.
Crimea, a region that Russia viewed as having been given away in similar suspicious circumstances as Yanukovych’s impeachment - where half of the voting party were absent - was seen as a dubiously given away gift to Ukraine.
A gift with extreme strategic importance to Russia’s naval operations in the Black sea and the sea of Azov, per the Russo-Turkish wars many centuries earlier. Russia were clearly wary of it falling into the wrong hands and potentially being used against them.
The West naturally condemned the move, with Russia declaring it was to allow the people to self-determine their futures. Russia saw what the US did in Ukraine as nothing short of a coup, an undemocratic effort.
Russia’s entry into Crimea was not without some democratic precedent: Russia declared they had been invited to take over by referendum, and the majority of formerly Ukrainian armed forces in Crimea defected to Russia, of which ~16,000 were re-employed by Russia to continue to defend the area. Not exactly violent invasion of the century.
Despite tens of thousands of armed people being involved, only three people in total were killed, one on the Russian side and two on the Ukrainian side, suggesting the takeover was largely peaceful and indeed democratic. A far cry from the violence in Kiev.
Russia declared it would abide by the later voting result of May 2014 in Ukraine, although judging by the referendum and defections in the thousands, it is clear Crimea wanted to remain with Russia.