Recently I looked at this chart. The height of the USSR was about 290 million. The US has a population of about 316 million source. Keep in mind, the USSR number is inflated because it is not just counting Russia.
Communism didn't work to well in the Soviet Union. Capitalism worked (and still does) in the US well.
Communism doesn't work in large groups because someone needs to decide how to spread the resources. It devolves into dictatorship often because of this. Capitalism works because individuals can make decisions for themselves. Therefore making democracy a easy option.
Yugoslavia had a population of 22 million source.
Yugoslavia acted differently than other communist establishments. It had democratic elections and monarchy was abolished, had local governments, and had quality standards of living.
Now for a capitalist example.
Switzerland has a population of 8 million source.
It has one of the best governments in Europe with many of the same qualitys of Yugoslavia (they arguably did them better). As you can see it is a small state which lays on the down low.
What do you think? Does communism work in small countries? Keep in mind correlation doesn't mean causation. The USSR and Yugoslavia also had different communism types (Marxist and Tito). Take this with a grain of salt.
EDIT: I meant to say countries in the title. Not country.