@Mad Black  
Somewhere along those lines. yep.

@Scrounge  
Right they say something like “[…]thos the two sisters maintained balance for their kingdom and their subjects,[…]”.

@Mad Black  
Unless I’m remembering it wrong, they called it one at the start of the first episode.

@Scrounge  
Did they call Equestria a kingdom in the show? I seriously can’t remember.

I think that ship sailed when the series started and they called Equestria a kingdom even though it was ruled over by Princess Celestia (and Luna’s return does nothing but make this weirder).

@Mad Black  
Good points!

Magisterium! What Twilight rules is a magisterium, not a kingdom.

The Crystal Empire has been ruled by a king and a princess. Never by an emperor. And whatever its own soverignty, it’s under the rule of Canterlot, which is also ruled by princesses.

SEIG SPARKLE

@Spiritus Arcane  
@Mr_Silence  
Even principality would be to big for a village like Ponyville. It is more like a Fief, maybe a Duchy if we count some of the surrounding area.  
The Chrystal Empire looks more like it would be a principality. But sonce Twilight is a princess her feudatory would be technically a principality.  
But Equestria is ruled by a princess, and it seems like a state of at least continental measurement, it would only be a principality. Even if it should be a kingdom, or even an (real) empire. Which would be fitting since empires can be ruled by a single empress (Celestia) or an oligarchy (all the Princesses together).

@Spiritus Arcane  
a kingdom is an area ruled by a king/queen like England & Saudi Arabia. A Principality is somewhere ruled by a Prince/Princess, like Monaco or Wales.

Isn’t a Principality just a type of kingdom?

Horse pun time.  
Prancipality.

Don’t you mean princesspality?

Then she would start a war for independence.

Nah, she don’t own either.

But then kids would have to learn what principality is! Also Twilight’s Kingdom is easier to say.