International law differs from national law in its aims, subjects, boundaries and deliberative bodies. National law is concerned with running a particular country and promoting the interests of its people. International law promotes the welfare of the entire international community, and has to respect the sovereignty of states.
The United Nations describes international law as defining the legal responsibilities that states have one to another. Sometimes this means that the issues it covers overlap with national law: immigration, global commerce and war. However, international law does not strive to benefit a single nation or group of nations. Thus, some of the objectives of international law can seem to be in conflict with the purposes of national law. For example, states typically build up their militaries and weapons stockpiles as a way of ensuring national security. International law, on the other hand, promotes mutual disarmament as a way of establishing peace.
The Legal Information Institute at Cornell University explains the sources of international law. Whereas national law is derived from state political bodies like parliaments and congresses, international law comes from international agreements. In a country, the government has the full force of a judicial system, police and military to enforce its laws. Because the international community strives to avoid war at all costs, economic sanctions are one of the few measures that can be used against transgressors of international law. As a result, international law is difficult to enforce. The United Nations Charter has established the International Court of Justice as its principal judicial organ.