Within international law--since the Peace of Westphalia created the modern international system in 1648--sovereignty is understood to be the quality of having complete and independent authority over a geographic area, most likely an entity with a monopoly on the use of force within that territory. Within the classical usage, the moral authority of the entity exercising that force (in the United States, that authority resting with "we the people") is important to true sovereignty. As understood within international law, a sovereign state maintains territorial integrity over its area, has borders that are to be inviolable by other states, and maintains supremacy in the making of laws within its boundaries. There are, of course, some exceptions to this definition such as the Holy See, the Knights of Malta, and Native American tribes, but the general idea is the same.
In response to the recent execution of convicted child rapist and murderer Humberto Leal Garcia, a Mexican national, by the state of Texas, United Nations Commissioner for Human Rights Navi Pillay has declared
that the state of Texas violated international law. Pillay referenced a ruling by the International Court of Justice in 2004 that ordered the United States to review and reconsider the cases of the 51 Mexican citizens on death row in the United States, including Garcia's (who was convicted of raping, mutilating, and murdering 16-year-old Adria Sauceda in 1994). As the United States rightly does not recognize the sovereignty of the International Court of Justice within its territory, as by law nothing can be higher than the laws of the U.S. Constitution, this order was ignored. Ignoring requests
from the Mexican government, President George W. Bush, and President Obama, Governor Rick Perry's press secretary said, "Texas is not bound by a foreign court's ruling." The United States Supreme Court declined to get involved.
Now, the United States is a signatory of the 1969 Vienna Convention on Consular Relations, which does stipulate foreign nationals must be put in contact with their embassies so that lawyers may be provided and their citizens looked after. However, in the 2008 Supreme Court case Medellin v. Texas, the 6-3 majority maintained its history of declaring that foreign treaties are not binding on domestic courts until domestic laws are passed in line with the treaty. President Obama, like President Bush before him, believed that America would be violating its treaty obligations if it executed foreign nationals without obeying the Vienna agreement. However, had President Obama really been concerned with the issue, then he would have known that the Supreme Court maintains American sovereignty within American territory and would have worked to, in the two years his party controlled Congress, make federal law in line with the obligations of the treaty.
Without arguing the merits of the death penalty itself (as that is an entirely different argument to get into), the real issue here is sovereignty. This man raped and murdered an American teenager on American soil, and thus he is subject to American law (and, in particular, Texan law). While we are signatories of the Vienna Convention, the Supreme Court is right to uphold the fact that the United States Constitution is the sovereign law of the land, and unless federal or state law is in line with an international treaty, that treaty's obligations are not applicable to domestic courts. Texas did not violate international law by executing Leal, as it was a domestic issue and international law is not sovereign over domestic courts. However, the governments of Mexico and Honduras do have legitimate complaints about the United States government violating their sovereignty
and breaking international and federal law
by arming malicious and murderous criminals in their nations with weapons that have been used to kill their government officials and citizens.