International Law has no meaning without international law enforcement. This is a hard reality that too many people refuse to face, but there is no law with no law enforcement.
If A enters into a contract with B, promising to trade ten thousand bucks in exchange for a car, and B accepts his ten thousand but does not hand over the car, B can go to the authorities who will, by force if necessary, fulfill their contract. If there is no authority to go to B's only recourse is to enforce the contract by whatever means are available to him (or just cut his losses).
In the international system there is no authority to enforce contracts (international law) between nations (and the UN definitely does NOT count) and therefore they are in the same boat as B in the example above. The quote from this post is particularly relevant:
"for you know as well as we that right, as the world goes, is only in question between equals in power, while the strong do what they can and the weak suffer what they must."
It matters not who is correct in the legal sense unless the two parties are equal (that is why the phrase "all people are equal before the law" is so important). So whenever someone invokes international law they are spouting out their ass not their mouth, because international law is meaningless without enforcement.
[I thought of a better excuse for creating a post out of that quote.. Yippee]