LAST MONTH Russia drove Ukrainian forces out of most of the territory in Russia’s Kursk region that they had seized the previous August. The Russians deployed their own elite brigades, North Korean troops and a new weapon—fibre-optic drones that are controlled by a long, lightweight filament rather than by radio signals, making them impossible to jam. Now the fighting has spilled back over the border into Ukraine. Settlements close to the frontier are being pummelled, and several thousand civilians have fled or been evacuated. Some Russian assault units have crossed the border—though so far, insists Volodymyr Artyukh, the head of Sumy province’s military administration, “they have been eliminated.”