Republic???????
With *THIS* level of war intensity, *NO* financial institutions (heck, do we even have currency?), zero military police, and zero troop support???
Madness, sheer madness (at this stage).
With the vile way our so-called neighbors have treated us, we're going to be in and out of war, likely against multiple civs at once.
There is one, and only one, justifiable government where we will be for a looooong time....
Monarchy.
The question is when? With the Golden Age behind us, there's one less compelling reason. We can't afford to switch with troops right outside major cities, or as we're assaulting a foreign nation's capital. I would (probably) wait for the peace lull, when we have less than eight or so civs at war with us.
IMO, of course, but it's a pretty strong opinion in this case

Charis