Why would the LORD cause his people to perish from the land?
Joshua 23:16 (ESV)
16if you transgress the covenant of the LORD your God, which he commanded you, and go and serve other gods and bow down to them. Then the anger of the LORD will be kindled against you, and you shall perish quickly from off the good land that he has given to you.”
If Israel rejects God’s commandments, this would cause God's anger to burn against them with the end result being expulsion from the land in keeping with the terms of the Mosaic covenant (Deuteronomy 28:63–68).
16 if you transgress the covenant of the LORD your God, which he commanded you, and go and serve other gods and bow down to them. Then the anger of the LORD will be kindled against you, and you shall perish quickly from off the good land that he has given to you.”