Rulebook says
“If an Army assaults a Population Center with the intent to destroy, then the troops of that Army will find that assault easier than if they had assaulted to capture.”
I can not find any other information about this issue.
From your experience, do you have any idea of how the difference plays on calculations ? (army strength, army constitution, PC defense ?)
And how much ? (1%, 5%, 10% ?)
it is a significant difference. As a rule of thumb, I’d say that if the combat calculator says you can capture a certain loyalty pop, you can destroy that pop with loyalty+20. What do others think?
I have no idea if this is right or not, but I’ve been going under the assumption that the only difference between capturing and destroying is that your trrops’ morale is bumped up to 100 for the combat vs. the pop center. So if your army morale is really low, I think that could make a big difference.
What has worked for me is: Inflate your troop strength 10% and increase your loyalty to 100%.
Ed, do you mean increase your morale to 100%?
My morale is 100.
I hope you are right for the troop strength increase 
Er, yes. Prooofing has always eluded me.
i think its commonly accepted that army morale goes to 100%. however, “commonly accepted” does not make it fact. destroy does make a rather large difference, esp. when you consider the importance of army morale in the combat math.
sm