Say,the three pony races would end up in a war AGAINST eachother, it brings up 2 questions, being:
1.Who would obviouslly be in the best place to win.
2.Which side should the royal familly choose?
The first thing you would say is that unicorns will win,which is natural. I mean,Pony with magical powers which can teleport itself/other ponies and turn ponies inti anything and protect themself with magical shields. But in the show,it is shown that some spells have a delay of hitting it target;meaning something fast and agile like a pegasus, which are fast, and can fly to places other races can't go. Unicorns are arguelly also the weakest considering they never used their muscles to lift or use power or strength. Earth ponies are doomed with using their hooves and mouth.
But the royal familly, would probally just flee to another land or try to reset peace alone, risking their lives. But which race they would prefer is.... beyond knowing