Not between countries at the state level. Even 'free trade' is a treaty obligation.
Countries can decide not to trade or interact with a given country which is their business. There is no obligation to do business with NK. And deciding to not do business with a country is not the same thing as an act of war. You are not saying that our actions have resulted in NK being able to say we have declared war on NK (which we haven't). Surely that's not your point.