Beyond the story of kingdoms; the previous century is evidence reasonable enough to evaluate how two great wars wrecked the world when each of the participants tended to invade the other. Diplomatic intervention perhaps led the states to face military invasion. Role of intervention in both the wars was to the extent that both League of Nations then and United Nations now corporate explicit principles in charters to respect sovereignty of states and not to intervene.
UN CHARTER ON INTERVENTION
Article#2(4) of the Charter is explicit enough to state; “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.”
Further; chapter#7 of the Charter deals entirely with the actions in respect of peace and aggression.