The same thing that SHOULD have stopped our meddling in Ukraine -- military force.
The Russians know they couldn't defend any troops they stationed in Cuba.
We should have known that there is no way we could win a proxy war in Ukraine.
BTW, I am perfectly consistent. If Russia or China were engaged in the kind of military buildup in Mexico or Cuba, I would be all for US invading.
We right now have troops, tanks, planes, and missiles in Poland, Finland, Estonia, Latvia, Lithuania, and Romania?
So what’s Russia going to do about it? Hmmm?