Ortalians are the perfect soldiers, but do not hesitate to bolster their ranks with a wide array of mechanized units. Executioner-class mech is but one they employ to annihilate Empire's enemies. Then Discord happens and steals a mech.
A group of misfit Chimera are transported to Equestria after the Battle of London. What do? Attack the royalty, that's what. To be honest, she started it.