You're a nation if you have a military. These folks clearly failed that test.
The question of "legally" invading someone's house is odd anyway, because legality implies some authority having deemed it appropriate. In the case of a neighbor's house, it is the government of the country containing the house. I can't think of an entity that establishes the "legal" way of creating/invading a country.
Of course this is all messed up. There's no reason a nation shouldn't be considered a nation just because it doesn't have a military.