There are no analogies in your abstract constructions. First, I have never heard if Lithuania has declared something like Monroe Doctrine of her own. Second, if you think it is about invasions in the first place you do clearly misunderstand the whole thing. In fact you are mostly misinterpreting not misunderstanding it because unlike other individuals with agenda trolling this type of threads, you seems like have IQ above their average.
If country A, a nuclear power, wants a “buffer” between it and another nuclear power, then why shouldn’t country B (a “buffer” target of country A), want protection against country A?