KYIV, Ukraine, and MOSCOW — When the Kremlin launched its all-out invasion of Ukraine in 2022, the assumption in Moscow, and much of the West, was that Russian forces would take the country in a matter of days. Instead, what the Kremlin calls a "special military operation" has become the biggest land war in Europe since World War II and has lasted longer than the Soviet army's fight against Nazi Germany. Russia's war on Ukraine is a grinding war of attrition. Ukraine has managed to hold a much larger army to minimal gains while adjusting to a life under constant...