in that way he will get maybe 8 MP while you can kill up to 40 000 his villagers (40 MP)...do it on 10 attacks,you have 400 MP he 80
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That will only happen if the enemy is a big farm. If they have 10 provinces and 200 villagers each you should be able to send enough siege to break everything.
The enemy gets 8 military points if the fortress is a level 5. Players using one level 5 fort should never be matched against players with 10 provinces and 2,000,000 villagers.