Adam Clarke on Joshua 9:15

Joshua made peace with them - Joshua agreed to receive them into a friendly connection with the Israelites, and to respect their lives and properties; and the elders of Israel bound themselves to the observance of it, and confirmed it with an oath. As the same words are used here as in Jos 9:6, we may suppose that the covenant was made in the ordinary way, a sacrifice being offered on the occasion, and its blood poured out before the Lord. See on Gen 15:10 (note), etc.