Station 4: Does the Old Testament contradict the New Testament?

Is God, "a man of war" (Exodus 15:3) or "the Lord of peace" (2 Thessalonians 3:16)
How are we to understand the stories that take place in Joshua and Judges? Did God really command them to kill whole cities?
This stems from a common attack nowadays which takes difficult passages like those in the Book of Judges and asks for an explanation, or takes some verses out of context to present a distorted image