Communism is supposed to be decentralized and democratic. I assume you mean the Soviet conception of communism was a traditional top-down rule from above. (It wasn't communism)
What is interesting is that once you look into it, it is structured similarly to some of the conglomerates (keiretsus) of Japan. Basically they have their own bank etc, in part because external banks were not interested in doing business with them.
It's clear that it's not necessary for a system to scale globally to be useful.
But a political system that scales globally is definitely desirable; an awful lot of human suffering is directly traceable to sub-optimal decisions made internationally because "those people" aren't "our people." There are big wins to be had for solving that problem.
