The short version: There is
no such thing as international law. (By definition of international, I mean every country in the world, as opposed to
interregional)
The long version: The reason for this is simply that there is no international police that can carry out sanctions on violators of the law.
No sane country in the world would want to give of it's soverignety to an international police force (For UN operations, see below). Remember; the definition of a state include the ability to use force (as in arresting and prosecuting) on it's people.
There are a lot of international treaties. These are a whole different ballgame. The treaties are higly practical in nature, such as agreements on shipping, distribution of airwaves and such. However, there's no such treaty that forbids a person to kill another, for example. The closest to possibly get to this is the Geneva convention on war crimes. The reason for this is almost the same as above, you can't impose your moral standards on everyone else. Each country has it's own way of dealing with crime, and wants to keep it that way. Remember; countries are amoral when it comes to international politics.
Treaties are binding for the country that signs it. However, a country can say yes to the text of a document and then refuse to ratify it. A good example of this is the US commitment to cut back on air pollution, which simply didn't happen this time.
On the other hand, a country can find ways of including a treaty in their own laws. This is done with international freight regulations. E.g.: If I send a package by truck from Norway to Spain, the law would remain almost equal in each country the package passed, due to the similarities in the national law which is based on the same treaties. And it's still not international law. One of the countries that takes this most seriously in thei law system is the US, where the constitution says that a treaty should be considered equal to "the law of the land".
The EU has a similar way of handeling this. It says that each country has to adapt their laws to fit the EU charter. But does that mean France can send police forces to Sweden if they don't follow the charter? No. That's why it's not international law. The sanctions are carried out on an economical basis, but are highly restricted to the countries that have signed the EU charter.
The UN does have peacekeeping forces, but they are military forces trained for military operations. If a person is to be prosecuted by the war crimes tribunal, the problem is to arrest him/her. That's why so few of the Jugoslav war criminals have been prosecuted.
Another interesting thing is the police officers from various countries operating in some parts of former Jugoslavia. They are given a UN mandate to stand in for the local police until the region is stable enough to govern itself. But the laws are local.
In response to the WU below: No. The international courts are voluntary. These courts can only decide in cases the indicted countries have agreed to, either in advance or on a case to case basis. The state leader argument must be considered a nullity here, since it bears no relevance to this discussion. What the AAL states, is irrelevant here. International Law is used as term used to describe the different treaties and agreements. That does not mean there is such a thing as a law that govern more than one state at a time, involuntary. Think of the EU. Do they have a parliament that govern all the different countries by single law? No. They have an agreement system that incoorporates the laws EU parliament passes. Each country can, at any given time, dump the treaty and ignore it at a minimal risk. None, actually, except for loss of international respect.
If you disagree /msg me and we'll discuss it in a civilized matter.