Siege. Starve out the enemy

 Traditional way to take castles, cities, and the like.  Surround them, cut off their supplies, and wait for their food to run out.  It has worked for thousands of years.  From what I see on TV (reliable that is) the Russians have not yet surrounded Kyiv.  Last general I remember who neglected this essential step was German general Paulus at Stalingrad.  He was defeated and he and his entire army was killed or captured.