After all, isn't this exactly the reason the Ruskies invaded Ukeland -- which started a major proxy war when Putin had no right to invade that country?
Fair enough, probably just what elementary school teachers around the U.S. are inviting students to examine.
But I will assume you are a functioning adult and suggest that it all comes down to self-defense, or more formally, "national security".
It is complicated by the fact that several or even all of the sovereign nations you might have in mind have indeed seduced, coerced, compromised, paid off or even bribed some or all of our most recent presidents; at least commencing with Clinton's first term in 1993.
My take isn’t exactly that, but close. The Russian’s rationale was partly the push for Ukraine to join NATA, thus removing a buffer state between Russia and NATO states, plus a claim that Ukraine was somehow a historic part of Russia. I can fully understand the former reasoning by just imagining Russia, China, Iran or some other adversary establishing military bases and/or alliances with Canada, Mexico or Cuba.
I’m personally against the proxy war. We don’t have national interests in Ukraine and if Europe has a problem with Russia’s invasion it is about time for them to pay their own way. I’m also for America leaving NATO, for many of the reasons Trump enumerated, but backed off.
The only parallel to Russian and Ukraine to China in Cuba is proximity, unless you see a proxy war developing. That is China using Cuba as a proxy. That seems doubtful. There still is a notion of the Monroe Doctrine, but really that was aimed at the Spanish and to a lesser degree European colonizers in general. But the idea of keeping nations out of the Western Hemisphere has failed, so there isn’t even that.
The China-Cuba spy base situation a better analog with the Cuban Missile Crisis, although not nearly as dire. It is a threat that needs to be dealt with. More than anything, I think it is China pushing to see how we respond. There are plenty of non-military means to respond and remove the threat.