I didn't really get the "borrow from the future" thing.
What I'm trying to say here is that I feel it is a bit stupid... u get money every turn even if u'r not taxing the shi*t out of your cities then you're called to war u raise a small defensive army booom your economy has shi*ted it's self? even if u still get money from your cities, not as much as u did when u did not have the army, but u still receive it.
This I don't get. Maybe I'm stupid. I love to micromanage cities. I love making bilions and recruting dozens of armies... but this... I don't know. I'm all for realism but I'm not sure about this.