[design flaw] 100% rebate on training time by combining faction and empire buildings
from
Elemental Forums
It works in theory and in practice. If you conquer a city of opposite allegiance and that city has buildings that reduce training time, you can add your buildings that reduce training time (since they have different names, they can combine each other) and you get a 100% reduction to training time which allow you to make any unit in 1 turn.