conduct relations with other nations according to its own standards and traditions.

Though such a critique is undoubtedly simplistic, it nonetheless contains enough truth to make it plausible. International law, of its very nature, does indeed involve a watering down of national sovereignty in that nations are subject to laws which did not originate with the relevant sovereign power. Even if the government of a specific territory was actively involving in framing the relevant law, it will still seem to many that such law is somehow being imposed on the sovereign nation by foreign powers. On this reading, sovereignty isn't so much being pooled as it is being diluted, to the detriment of the nation's right to make its own laws.

It was just such an attitude that ultimately did in the United States' proposed membership of the League of Nations. Public opposition to American membership of the League was very strong and manifested itself in equally fierce opposition at the Congressional level. The sovereignty of the United States as a free and independent nation was held to be under threat, and so the League of Nations, and the principles of international law it embodied, was decisively rejected by the American people and their political representatives.

The main limitation of international law is that there are no enforcement mechanisms. International law is used to keep the peace and to create rules for environmental maintenance, but it can only do this through a consensus of nations. Nations are free to decide whether or not to sign on to agreements. If a nation decides to leave an agreement, there is little that an international body can do that offers real punishment.

The League of Nations represents a failure in the field of international law. The League, the brainchild of Woodrow Wilson, never had the support of the United States, as many in Congress feared that the US would lose sovereignty over its own affairs. The League of Nations was designed to arbitrate between conflicting nations in order to prevent another world war. When Japan was criticized for invading fellow League member China, Japan simply left the League.

International law only has true power if it has enforcement mechanisms to punish countries who violate it. Many nations do not wish to give up troops in cases where their individual nations would not benefit from a war. Nations also will not sign on to sanctions without looking at their own interests first. While international law has many lofty ideals, its lack of enforcement makes it limited in terms of real power.

First, let's talk about what international law IS before we go about figuring out its limitations.  Stated simply, international law has the purpose of letting many nations keep the peace, protect human rights, and maintain productivity in both business and personal affairs.

International Law is the set of rules generally regarded and accepted as binding in relations between states and between nations. It serves as a framework for the practice of stable and organized international relations. International law differs from state-based legal systems in that it is primarily applicable to countries rather than to private citizens.

There are MAJOR limitations here.  Mostly, each country is a sovereign unto itself, so it is not binding with domestic governments!  In other words, international law is always just a "suggestion" and contains no "world police" to enforce its rules.  Even though there is a declaration of human rights that is universal, the only way infractions can be enforce is if a group of countries agree to enforce it.  This is often the way the United States gets blamed for "unilateralism." 

The United Nations is a perfect example.  The enforcement procedures are maintained through the Security Council.  There can be loss of legal rights and privileges within the UN and, if countries agree, peacekeeping forces can be sent to different countries, but there are so many countries with so many cultural differences, the UN is often rendered "useless."

Let's create a simply list as to why.  These, then, are the main limitations of international law:

1. need for consensus
2. no single international "ruler"
3. no enforcement mechanism ("world police")
4. lack of funding
5. vast differences in cultures, no real "norms"

Perhaps ICJ (International Court of Justice) could be considered  a successful organization of international law.  At least this body can make decisions in regards to serious war crimes.  (Milosevic is an example).  Decisions aren't binding, though.  So the limitations above still hold true. Further, there are too many dictators and other soverigns that simply ignore the international law organizations and, because there is no enforcement, they can get away with it.

Therefore, unless legislation under international law is enforced by domestic legislation (in a particular country) there is no one to enforce it unless a huge consensus is reached in international law agency, such as the UN.  Therefore the fight for world-wide human rights continues to be an issue in many areas around the world.