I chose the wrong word. 'civilized' is far too broad. It could refer to good taste in wine pairings, or grey poupon. Too broad.
I think the proverbial "line" is when a country is openly attempting to eliminate another country. To bomb it back to the stone age, killing innocent citizens including women and children, assassinate its leader, steal its land, its wealth, and absorb it.
There are many examples of conflicts between countries, and there always will be. There are many examples of state sponsored incivility and there always will be. Countries are not only awful to other countries, but they are also awful to their own people.
When countries get together at the Olympics, in a statement of unity and mutual sporting respect, it is symbolic of a higher level of peace and understanding. I believe any country that is trying to 'eliminate' another one of those countries should not be allowed to participate. It would go against everything the event stands for. The Olympic games aren't simply a competition, they are much more than that.