Armin is already aware that there will be wars even after his death. As a general, he leads, he does the tactical planning, and he is responsible for his decisions that affect the entire military organization.

As a soldier, you expect the worst to come. People were dying, people were killing each other, and so many horrid things happened just because of the war that was still going. So when Armin saw you hiding—a lonely child, away from danger—his heart broke.  "You’re safe now." He speaks.