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Ment, but this effect could also be added as an enhancement to an existing building. For example, the "Gates of Chaos" building. Considering that the building only requires level 3, it would work perfectly.
New buildings can only be added as dependencies. Therefore, you will have to build something "before" it, but not necessarily in a single stack.
However, the build tree is already visually very crowded, so some buildings will likely still need to be stacked.
Added 7 minutes later:
For example, you could add an upgrade to the tavern. Heroes are purchased with a tripled army, the garrison's defense is increased even further because there is now even more beer, or some other bonus.