This seems really simple, but how much force (minimum) does it take to destroy a province with 6 strength?
Taking a Province
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Your attacking army needs to have a total Force higher than the defending army's (if any) plus 6. Thus if the province is undefended, your army needs a total Force of 7 or more.
Battles, Resolution Segment: If the Attacker Wins: [...] 2. If the attacking army's Force was greater than the defending army’s Force plus the Province Strength of the province the current battlefield is associated with, the Attacker destroys the province.