idea about how it could work:


Either it take 1 turn to kill every population. That would mean with 16 population = 16 Turns, to raze the planet.


Or this I would prefer more: 


------ 1 

attackers: 3000 Manpower


Defender: 300 Manpower

Population 6


Attacker overhelm the defenders. Defender got nowhere to run and get killed. So the attacker move swift with numbers. Would take 1  turn or so.


------ 2

Attackers: 300 MP


Defender: 100 MP

Population 16


Attackers struggle to win the battle. Eventual they win and then they got a lot of civilians run and flee to the nearest planet. While the attackers destroys everything and kill anyone. 


This is just an exempel.


Not sure where this would go on the Tech tree. Or if it could be an option to give the soldiers in field. Give an ship commander an direct order perheps. And every Ship Commander are Human(At least for the UE) so they can also defy an order, Option? Resign or kill the Commander. Could be to complicated of course.