In 1992, the United States ratified the International Covenant on Civil and Political Rights (ICCPR). Article 6, Section 5 of the ICCPR states, "Sentence of death shall not be imposed for crimes committed by persons below eighteen years of age and shall not be carried out on pregnant women." Today the Supreme Court brought the United States into conformity with this provision of international human rights law by ruling, in a 5-4 decision, that the use of the death penalty for sixteen- and seventeen-year-olds violates the Eighth Amendment. (Those under sixteen were exempted in a 1988 Supreme Court decision from the imposition of the death penalty.) The Court's ruling sets aside the death penalty in approximately seventy cases nationwide.
How did the United States manage to evade this provision of international human rights law for so long? In 1992, when the Senate gave its advice and consent to the ratification of the ICCPR, it attached a number of reservations, understandings, and declarations (RUDs). One of the reservations stated, "[T]he United States reserves the right, subject to its Constitutional constraints, to impose capital punishment on any person (other than a pregnant woman) duly convicted under existing or future laws permitting the imposition of capital punishment, including such punishment for crimes committed by persons below eighteen years of age." This reservation was an embarrassment to the United States at the time of the ICCPR's ratification. The Supreme Court has performed a noteworthy service by making it moot.
One has to wonder why the United States Senate can't simply have more respect for international human rights norms rather than assuming that if we do it here (at least in a few states), it can't be wrong.