Most governments do not take seriously their obligations under international law, and certainly the United States does not. To U.S. policy makers international law is for everyone else to follow, and for Washington to manipulate when possible, or to ignore otherwise. Thus when the World Court told the United States to cease its contra war against Nicaragua and pay reparations, U.S. officials simply declared they did not consider themselves bound by the ruling.
There is a fundamental difference between law and ethics. The law is of no use without the individual being willing to adhere to it. What is the point of arms limitation treaties if there is no desire for peace?