Don't forget that Karl Marx said that somewhere does not just "become" communist as it will not work, but rather a socialist state will gradually and organically become communist over a lengthy period of time.
I'm inclined to agree with that, if we woke up communist tomorrow it would be a disaster, for it to succeed it would have to be via a protracted, lengthy change that would probably take longer than our own lifetimes.
There has never been a communist state (even the very term 'communist state' is an oxymoron), despite what certain states have claimed over the past century, and if there ever will be one (of which I'm not convinced), it will not be for many, many years.