This book attempts to wrestle with the questions as to how God could command the conquest of Canaan, and the subsequent violence.
Brueggemann is a critical scholar, and so doesn't see the text to be fully reliable as God's word. This aside, he still has a rather disappointing conclusion after 60 pages. He concludes (rather hastily) that the Canaanites who lived in Canaan, were technologically superior (with chariots) to the Israelites and so in fact were engaged in domination. This made it acceptable for Israel to conquer the land - and we now have to ask ourselves, have we become a part of domination in the world today?
This conclusion, doesn't really seem to do the text justice. Nor does it satisfy objections as to how God could command the slaughter in Canaan.
If you're looking for a better scholarly introduction, I heartily recommend the Grove Booklet by Philip Jenson, "The Problem of War in the Old Testament". Christopher J. H. Wright's The God I Don't Understand is also useful.