In 1 Samuel 15:2-3 , God commanded Saul and the Israelites, “This is what the LORD Almighty says: 'I will punish the Amalekites for what they did to Israel when they waylaid them as they came up from Egypt. Now go, attack the Amalekites and totally destroy everything that belongs to them. Do not spare them; put to death men and women, children and infants, cattle and sheep, camels and donkeys.'" Read more:http://www.gotquestions.org/Canaanites-extermination.html#ixzz3FapcfbhK
This is not a dispassionate account of one tribe wiping out another. It was under God's command.