Capitals and What they do!

[Lamech]

Alright then capitals are important, but what can they all do? So, I'm starting a list of references in the comic for the powers they have mentioned. If anyone has anything else they know, or speculation feel free to talk about it.

Alright then you need a capital for a barbarian to start a side.
When ruins are rebuilt a capital decides what they pop.
Units can be promoted to warlord in the capital.

I'll try to get the links when I have time, this is just what I recall. Also note, IMO I think that a lot of things we don't know if its a capital issue or a having one city issue.

[0beron]

A Capital is required to maintain a Treasury.

[Nnelg]

A Capital is required to maintain a Treasury.

IIRC Jillian had a purse as a barbarian; however it was very small.

[0beron]

IIRC Jillian had a purse as a barbarian; however it was very small.

Correct, Purses and Treasuries are very different things. A Purse is limited in maximum size, and as I understand, only pays upkeep for units the commander is stacked with.
A treasury is like a bank account for the entire side, that collects income from every city and pays upkeep for all units no matter where they are.

EDIT: Purses have the advantage of being much prettier, if a good Dollamancer is involved in their creation :p

[drachefly]

Leaders popped in the capitol of a royal side are themselves royal.

[0beron]

Leaders popped in the capitol of a royal side are themselves royal.

Not always though, right? Hasn't it been suggested that Warlords/Casters on a Royal side do not always pop as Royal/Noble? (Example, I believe it was clearly stated Ace is not Royal or Noble) However I don't believe we know if this is random chance or chosen by the Ruler when popping begins.
In either event, we DO know that the Capital of a Royal side is the only place Royals CAN be popped, units popped elsewhere would only be noble.

[Saladman]

From the glossary of the printed Book 1. Apologies if I'm going overboard, but some of this keeps coming up for people who haven't seen it, so I figured I'd throw out anything relevant while I had the book out.

Capital
A city which represents a side. It often bears the same name as the side, and is usually its most powerful stronghold. Each side can only have one capital. A capital is necessary for a side to have a treasury.

City
A specific location that is fortified and can produce units; cities are not merely collections of buildings. Cities may be small outposts consisting only of a garrison, or complex citadels with many zones and fortifications. This is indicated by a level between one and five.

City site
A location at which a city may exist. Very few hexes can contain a city, and only a scant few of those can contain a capital.

Garrison
1. The name for a city's central structure, or zone. If the garrison is taken over, the city is captured.
2. A category of units assigned to a single city. A garrison unit has 0 move.

Magic Kingdom
A location where casters congregate and trade services. The Magic Kingdom is accessible only through magical portals, most often located in a capital city.

Noble
A Commander unit popped to a royal side, in a city other than the capital.

Overlord
A ruler with no Royal or Noble lineage.

Treasury
A non-physical function of natural Moneymancy in a capital. The treasury holds a side's total accumulated Schmuckers.

Upkeep
The cost of keeping a unit around for another turn. Upkeep is subtracted from the treasury or purse at the start of turn.

Zone
A specific part of a hex or city such as tunnels or airspace.

[Saladman]

So, commentary. The converse of the Noble definition is that commanders popped to a royal side in the capital are royal, and the choice is only heir or non-, as Drachefly says. And Ace was described only as a non-Royal caster, so there's no conflict there.

Its most likely non-royal family as with the Firebaughs works by a parallel mechanic, that Overlords pop children only (and necessarily) in their capital.

Overlords are defined as neither Royal nor Noble; the one case we haven't seen on-screen is a Noble ruler; the one title we haven't seen on-screen is Regent (as in the Regency of Hyatt mentioned in book 1). I speculate that Regents are Nobles named as heirs who succeed to Ruler-ship. It has the advantage of tying off the two loose cases we know about, rather than requiring two more cases unknown and unmentioned if Noble rulers aren't Regents. Possibly they're an exception to children in the capital, and capital commanders they pop are Royal again (raising an awkward relationship), but now I'm speculating without any basis.