Be forewarned that there are major spoilers ahead.
In Star Trek Beyond, we find out that
the villain Krall is actually a human: Captain Balthazar Edison of the USS Franklin, who served in Starfleet at the beginning of the Federation and was previously a MACO who fought in the Xindi and Romulan wars, earning respect as a hero.
As I recall, the only MACOs who actually saw action in the Xindi campaign were the ones assigned to Archer's ship.
This leads me to ask:
Did Krall serve aboard Archer's Enterprise?