This they did cover, through the alcoholic guy. Everyone on Earth was lied to. The Martians curbstompped Earth's military with probably just a single Cataphract. It was likely over in an instant.
But then I can't explain what made them sign a peace treaty, sure, the hypergate exploded - but why? Earths technology isn't that advanced, the mechs were created after the first war if I'm not mistaken. So how did they even send military forces to the moon... on top of that, they must have managed to pass all the martian fortifications orbiting around earth (Knight-castles)