Comment by true_religion

Moats were there to protect your castle which had your military and the supplies to keep them fed.

If you go to guerrilla warfare immediately, you’re basically now forced to face the enemy on the field on even ground even when you are on the defense.

All they have to do is burn your lands, destroy your fields, kill your civilians and you have lost.

They’ll do all that and safely retreat back home leaving you defanged.

That’s what medieval warfare was all about. Not absolute surrender and conquest, just temporary suppression and maybe forcing your enemy to pay your tribute.