Which is why IMTU the Imperium used ortillery strikes until Earth surrendered unconditionally . . .  e.g. VERY precise deep-penetration strikes on defenses and subsurface bunkers, which nevertheless incurred significant civilian casualties, destroyed countless Solomani cultural icons and resulted in enough global climate change to (over time) change the world into a desert planet.

[Which final consequence allows current-day denizens of MTU to refer to "Earth That Was" . . . :)]