One month into Russia's invasion of Ukraine, fire rained down on a shopping mall and high-rise buildings in Kyiv, as the outnumbered Ukrainian military waged intense battles to defend the capital and other key cities from falling under Russian control.

A barrage of strikes on cities have wreaked destruction across Ukraine over the past four weeks, but Russian forces appeared stalled outside major cities in the face of fiercer-than-expected Ukrainian resistance. NATO estimated on Wednesday that 7,000 to 15,000 Russian soldiers have been killed since the war started Feb. 24.

On Wednesday, the U....