Sovereignty, the Border, and the Law of Nations
Securing one's borders is the responsibility of sovereign states in the modern world. Those that are unable or unwilling to do so are failing in their responsibilities as nations. Along the border between the U.S. and Mexico, the people who are failing to keep law and order are not the Americans. According to the logic of the law of nations, therefore, the U.S. is well within its rights to inform the governent of Mexico that if it is unable or unwilling to secure its own border the U.S. will do it, and, while doing so, it may assert the right to enter what is formally (although not, as the facts make clear, in fact) Mexican territory. A century ago, that logic would have been clear to just about everyone in the U.S. government. Nowadays, few, if any, recognize it. Not sure that change is all to the good.