Not a player controlled country. But a computer controlled one yes it is. If you already have a country on that same world it will cost you 300 GC's. example if you have a country on KB and want another one without any war it will cost you 300 gc's. The one country becomes your leader and the other than becomes your slave.
If your on KB and want another country on say Golden Rainbow it will cost 30 gc's but then every month after that you have to pay 30 gc's to maintain your country or empire on Golden Rainbow.