The last sentence of the passage is:
"A hospital alone shows what war is."
What the sentence tries to explain is that it is in hospitals where we can truly see the effects of war. Hospitals allow us to see the great destruction and death that the war brings. They also allow us to understand the extent and scale of the war, as thousands of bodies arrive in thousands of hospitals. The author believes that the hospitals make you realize how pointless, cruel and overwhelming war truly is.