Marathon: How One Battle Changed Western Civilization by Richard A Billows

I finished "Marathon: How one battle changed west. civ" by Richard A. Billows. It was good, but of the 200+ pgs, only 30 were about the battle, w/ the rest devoted to centuries of Greek/Persian history. Some background is always nice, but you don't need to know the history of bratwurst making to understand how Rommel fought, do you? So why should I care about similar minutiae in Greek history?