Pony Of Mass Destruction-Short version, do not piss off an alicorn. Don’t make them angry enough that they want to break out the entire toybox of means they can deal with threats. The weakest and youngest of all alicorns, Prince Lucifer Morningstar, once picked off battleships from the surface of the planet he was on. Without a magical amplifier, killing each ship with single shots. He was tired when he was done, but that was about eight battleships later.
What one of the older alicorns could do almost beggars the imagination. In theory, Princess Celestia could turn Equestria’s sun into a Lensman-scale sunbeam. Princess Luna could drive you mad in your nightmares that would never end, even if you were wide awake. Princess Cadence, the weakest of the four eldest ponies, could destroy every feeling of love and loyalty you ever had (and this is a state secret so high even other alicorns don’t know about this). And, Princess Twilight Sparkle? She’s the head of the Ministry of Magic, one of the three ponies in charge of the Ministry of Ghosts, and has access to all the toys.
(Also, they have control, as much as sheer power. Any “Fall of Equestra”-type situation would end in this universe by the simple fact that Celestia could and would teleport instantly a pinprick sized piece of stellar plasma into the heads of every invading Caribou. Tiny pin-prick sized piece, just enough to reduce their heads to an instant cloud of floating red mist…)
Equestriaverse 
Y’know, I was reading this story – http://www.fimfiction.net/story/207626/1/twilights-sputnik/orbital-mechanics-for-pony-princesses – and kicking around, as one does, some numbers on the hypotheticalverse assumption that the Equestrian solar system is relatively conventional but possesses some unfortunate instabilities (seems more likely than Canterlot bureaucrats; and, well, easy enough to blame on the Discord era) that require the Two Sisters to keep manually managing planetary/lunar rotations and orbits, and quite possibly also keeping a flare-prone sun in order.
The answers you get about the sheer quantity of power packed into an instrumentality the size of an alicorn’s horn in this case have some quite remarkable exponents in them.
(I wouldn’t argue with them, either.)
…it also makes it pretty easy to explain why anyone else in the stellar neighborhood might choose to pay a visit to the system, for that matter. Hello, major gravity wave anomalies, nice to meetcha!
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