Long ago the names of countries were given by the Kings or intellectual leaders at that time. Often the name of country was chosen as the name of the region of in the country was located. It was Related to ethnicity too,
When a revolution took place and new type of government was formed like it happened in case of USA, Russia, China, etc., the new names were chosen by the leaders.
The name contains words like : communist, republic, socialist, people, democratic etc. That means the political philosophy adopted by the country, when it was born or reorganized in a major way.