This is how I understand it. “This battle is not only [about] the victory or defeat of the nation; it’s up [to this] to determine which, of each and every person, is chosen.” Here, I’m intepreting「Ｘに委ねている」to mean “it’s up to X” (lit. “it has been entrusted to X”), but the X is implicit.

“This battle is not only [about] the victory or defeat of the nation; each and every person has entrusted [to this] which [side] to choose.”