Cause ull have a ton of ally plunder bonus from all guilds but since spues cant use plunder u need the one forge
After you buy ur 18th land( for now go all forges) start converting to level 3 guilds one at a time keeping ally plunder maxed then once you land complete upgrade all ur guilds to level 4 and destroy the forge and build a subterrainian factory and upgrade to level 3
The best money making build is 24 lv4 guilds, a sub factory, and max plunder in allies. Has greastes capacity to make money out of all the builds. In theory.
However, in application it is vital to have a farm to hit endlessly in order to obtain max plunder. That is why this build is only reccommended should one have either a clan or a pure spy one can hit without retaliation.
Buy allies, ATM I don't have the numbers on me, but this build could make you millions per hit...lv4 guild is 432k plunder, times 24...you get the idea.