What Was One Consequence of the Thirty Years' War, Especially

What was one consequence of the Thirty Years' War, especially among those who wrote about the laws of war and peace?

A) an increasing focus on what made a war just or unjust in the first place
B) a new call for far less organized national forces
C) the acceptance that large-scale slaughter was an unavoidable part of war
D) the idea of war as a game
E) a growing concern with the conduct of war