Communism and capitalism are worldwide economic systems, not ideologies or govermnent styles. Capitalism is the way human relations and the exchange of goods work in this era. A so-called communist country would still live in a capitalist world, even if it isolated itself from the rest of the planet like, say, the DPKR does, they still would have to participate in the market relationships with other countries.

Socialism, on the other hand, may be possible to a certain degree under capitalism as a transitive system. The same way there were transitional proto-capitalist efforts in several western countries towards the end of feudalism.