In the modern times, no state can survive in isolation and no state can ignore the involvement in international sphere. This involvement must be systematic and based on some well-defined principles. So, such kind of principles in the light of that such involvements are made is called Foreign Policy.
Nation state system is as old as the human history. It will be more correct to say that the history of nation state system starts with the political consciousness of man. In this modern age, no one can satisfy its all needs alone and due to this lie has to make relations with other states in order to satisfy his desires, interests and goals. In the field of international politics these states are called sovereign states or nation state system.
When the concerned States fail in settling a dispute by peaceful means, forcible or coercive means are adopted. These are Retorsion, then Reprisal, Intervention, Blockade war.According to J.G.Starke, retorsion is relation by a state against Retorsion discourteous or inequitable acts of another state such retaliation.