Russia regards Ukraine as being in her “sphere of influence”. Russia has long regarded Ukraine as “South Russia”, or some territory that should really be Russian; hence centuries of intermittent attempts at genocide against Ukrainians and Russification of the region. It’s the genocides and Russification of the Ukraine why there are even that many Russians there today.
That said, NATO has been expanding toward Russia ever since the Cold War ended, and Ukraine herself was a target for NATO expansion, and probably eventual EU membership—Russia wasn’t going to idly stand by and let that happen.
Had the venal neoliberal crooks and bandits not forced Gorbachov’s hand back around 1990, and forced Russia to “liberalise” its economy (Gorbachov naively thought he’d be free to pursue a Nordic style of social-democratic economic development in Russia) it would now perhaps not be run by the Mafia, oligarchs, and “Tsar” Putin.
Not an argument to condone Russia, but her sphere of influence, and her imperialist ambitions and adventures, are largely contained to neighbouring countries—unlike the USA, which acts like it owns the whole world.