Do you know how to play chess? If you do, then you know you have to think like a bunch of moves in advance. Cuba for them was an advanced move. Being on our doorsteps, as the Cuban missile crisis demonstrated, it had all kinds of leverage opportunity for the future.There were a lot of unknowns. They were wrong on stuff and we were wrong on stuff. Domino theory was widely believed but it's since been discredited. No need to go back to it.
And if their business plan was to take over a lot of countries and seize their resources, they should have been better businessmen. At least after world war II. They were paying millions which would be billions today to prop up Cuba and North Korean economies. Vietnam played Russia against China.
If they were really hoping to take over countries and seize their resources, they should have been using Britain and the US as a model. We knew how to keep those communists out and keep countries free. Free to sell us oil and bananas.
Gaining leverage is the name of the game. And they were definitely intent on gaining leverage over us for blackmail, resources, and all kinds of advantages. Their corrupt system depended on it for survival.
Come to think of it, Putin is doing the same thing. And of course we seek to gain leverage all over the place too. Just our capitalistic less corrupt system allows us to do it in a different way as you alluded to.