French and English soldiers
The allied forces are dug into trenches. As the depiction of the battle fades from color to black and white, these men are drained of their hope for victory, and then of their hope for survival. Before WWI, no one had experienced the problems of trench warfare, so as the characters experience this death trap in real time, the reader witnesses it too through artistic renderings.
German forces
The Germans are shown as the archetypal enemy. They are constantly harassing the troops as they attempt to organize, and so the German military becomes a bane against them. They hate the Germans, but it's hard to get close enough to the enemy to kill them. The Germans are experiencing many of the same problems in the inverse way, but sometimes their machinery or chemical warfare helps them to keep a slight advantage.
Military leaders
The story shows the leadership of the Allied forces as it struggles to make sense of new kinds of warfare. The problems of WWI are so out of the ordinary compared to their experience and training that they often make poor decisions. They send soldiers to certain death in no man's land. When new leaders come into the battle, they are even less educated about the battle than the soldiers themselves, but they still command the petty ranks.
