UN members last month failed to reach agreement on the Arms Trade Treaty after a month-long conference. This is the latest setback in a decades old attempt to control the trade in small arms. A broad network of states, NGOs, and the UN bureaucracy had pushed for the treaty and earlier measures. In their view, proliferation of guns contributes to hundreds of thousands of casualties per year in conflict zones and to large numbers of shooting deaths in countries at peace. But the international campaign to control the illicit trade in small arms has long faced skepticism from certain states,...