Godzilla Threshold-What happens when an alicorn becomes involved in any major armed conflict. Prior to the Horizon War was the Battle for NuDawn, when a Changeling force attacked NuDawn.
The planet only had one real defense-Prince Lucifer Morningstar was there because he was visiting a penpal. Once the Changeling fleet came into orbit, he moved immediately to the opposite side of the planet and…waited.
Every time a Changeling ship came over the visual horizon, he destroyed it in a single strike. Before the fleet broke orbit-and it should be noted, didn’t take a single pony-he had destroyed over twenty battleships and similar numbers of supporting ships. The Changelings tried to kill him with a saturation kinetic energy bombardment-which he stopped before any weapon went past the troposphere. At the end, he teleported back and was hungry and tired, but indicated that he could keep going.
Lucifer Morningstar is one of the youngest of the alicorns, and the moment they realized that one of them was on the world, the Changeling Queen left.
What the Four Eldest could do is terrifying to any rational invasion planner. It is considered that short of a re-appearance of the Precursors, any invasion of the Equestrian solar system would be brief.