The Vanguard of Hell. Humanity's mightiest military as of 3182 Third Age (BC, or Second Age, ended in 6047 BC, and the year after was 1 Third Age, for reference). Their massive ships and their powerful, armored Vanguard Marines prove more than a sturdy defense against the alien hordes that want nothing more than to destroy us. When a Vanguard Mega-Cruiser, the VONS Ram Of Your Gates, crash lands on Equestria, drawing the attention of the hostile S'riiv'ya Empire, the confused human soldiers and the even more confused pony residents must learn to work side by side if either are to make it out alive.
Also, what the Vanguard Marines look like:
http://snowy-aegis.deviantart.com/art/Vanguard-435854388