The United Nations General Assembly on Tuesday signed off on a sweeping, first-of-its-kind treaty to regulate the international arms trade, brushing aside worries from U.S. gun rights advocates that the pact could lead to a national firearms registry and disrupt the American gun market. The long-debated U.N. Arms Trade Treaty (ATT) requires countries to regulate and control the export of weaponry such as battle tanks, combat vehicles and aircraft and attack helicopters, as well as parts and ammunition for such weapons. It also provides that signatories will not violate arms embargoes, international treaties regarding illicit trafficking, or sell weaponry to...