In the US this term is used to distinguish a country's government from its people. It refers specifically to a person or enterprise acting at the direction or as part of a country's government or military, as opposed to a private citizen. That's an important distinction in a country obsessed with protecting civil rights where nationality is a protected class. Under US law, preventing the purchase of a house based on national origin is unconstitutional. But if they are acting on behalf of a foreign government... You get the idea.