Or 1 million soldiers die from friendly fire, starvation, environmental conditions (freezing), overdosing, disease, infighting, and general injury from poor troop movement/management with a complete breakdown of supply lines.

Attrition is a major soldier killer. Its most effective when an army is undersupplied, unprepared, and undisciplined.

Guess what the Russian army is.

All of that also ignores that zerging doesnt work when attempting to occupy a location. When the guerrilla civilian fighters are better equipped both with weapons, equipment, intelligence, and communications, you have a serious problem. Theres a reason you dont invade cities. A city on the defensive is at a significant advantage vs an invading force.