"państwo" is rather "ladies and genlemen", for a mixed group (or sometimes, in writing, you don't know exactly who will read it so you write "szanowni państwo")
But apart from that, it's also a country. Well, "a state" could be a closer translation politically (and I don't mean a state like Texas, but a state like Venezuela or Burkina Faso), but in everyday language I think English just uses "country" and Polish doesn't care much about the technical differences between "państwo" and "kraj".
Does that mean that "These people only sell gas" is a valid translation, if you're discussing a group of ladies and gentlemen?
No. Then this word is plural, 'masculine personal plural', and therefore it would be "Ci państwo sprzedają tylko gaz".
Republic? Why? It's not a synonym of "country", not all countries are republics...
Well, and "the country" may be either United States or the countryside. Words have different meanings ;) Yeah, I get your point. Those are just two words that happen to look identical.
Country could be translated to "państwo" or "kraj". In this question there must be nominative, so there's no change in form.