The remainder of Joshua 10 provides a list of the other cities and their kings whom the Israelites conquered in the southern portion of Canaan. The Israelites fought battle after battle, never losing to their enemies since God was with them and made them successful. They left no survivors. Although the names of these cities may mean little to us today (e.g., Libnah, Lachish, Gezer, Eglon, etc.), each one represented a community of idolaters who were involved in wickedness which God could not tolerate any longer. Thus, they were destroyed in accordance with God's will through Israel, and their land and possessions were given to Israel in harmony with the promise God had made to Abraham centuries earlier. "So Joshua conquered all the land: the mountain country and the South and the lowland and the wilderness slopes, and all their kings; he left none remaining, but utterly destroyed all that breathed, as the LORD God of Israel had commanded" (Josh. 10:40). There is nothing unethical about the Israelites' behavior here. They are following the orders of the Most High God, and certainly He--as Creator and Sustainer of the Universe--has the right to inflict vengeance against wicked people in the manner in which He chooses (e.g., Gen. 6:5-7; II Thess. 1:7-9; Rev. 21:8).
As Chapter 11 opens, the Canaanite kings of the North heard about the destruction Israel was inflicting in the South and they decided to band together and attack Israel. "So they went out, they and all their armies with them, as many people as the sand that is on the seashore in multitude, with very many horses and chariots" (Josh. 11:4). One might suppose such large numbers would intimidate the Israelites, but God gives the order to attack courageously and the people do so. "So Joshua and all the people of war with him came against them suddenly by the waters of Merom, and they attacked them. And the LORD delivered them into the hand of Israel, who defeated them and chased them...they attacked them until they left none of them remaining. So Joshua did to them as they LORD had told him: he hamstrung their horses and burned their chariots with fire" (Josh. 11:7-9). A numerically superior enemy is no problem for Jehovah! But why destroy great military weapons like horses and chariots? Because God wanted the people to continue trusting in Him, not things (cf. Deut. 17:16; Psa. 20:7)! Besides, how much good did the horses and chariots do for the Canaanites?!
"As the LORD had commanded Moses his servant, so Moses commanded Joshua, and so Joshua did. He left nothing undone of all that the LORD had commanded Moses. Thus Joshua took all this land: the mountain country, all the South, all the land of Goshen, the lowland, and the Jordan plain--the mountains of Israel and its lowlands...He captured all their kings, and struck them down and killed them. Joshua made war a long time with all those kings. There was not a city that made peace with the children of Israel, except the Hivites, the inhabitants of Gibeon. All the others they took in battle. For it was of the LORD to harden their hearts, that they should come against Israel in battle, that He might utterly destroy them, and that they might receive no mercy, but that He might destroy them, as the LORD had commanded Moses" (11:15-20).
Joshua 12 is a summary listing of the 2 kings Moses conquered to the east of the Jordan River and the 31 kings Joshua conquered to the west of the Jordan. Some have estimated that several decades are spanned in these chapters. Regardless of the amount of time covered, these chapters reiterate a common Biblical theme--trust and obey the Lord in all things and you will be blessed with victory! Furthermore, there is a time for everything--including war (cf. Eccl. 3:8).