Cluster weapons—those mini-bombs that have cost many a civilian their foot or their life—are back. Russia has just unveiled what it describes as a stealth cluster bomb. This comes after the Trump administration scrapped a plan to eliminate cluster weapons by 2019, despite 103 nations signing on to an international agreement to ban production and use of such weapons. So far, 120 nations have joined the 2008 Convention on Cluster Munitions, of which 103 have actually ratified it. Unfortunately, the two biggest arms exporters in the world—America and Russia—have yet to join. Russia is testing the PBK-500U glide bomb, a...